Thousands of cheering Yemenis today greeted the female student detained briefly on suspicion of having sent two parcel bombs found on US-bound planes last week.
Yemeni police arrested computer science student Hanan al Samawi on Friday after tracing her through a telephone number left with a freight company but released her the next day, saying she had been a victim of identity theft.
Ms al Samawi, accompanied by her father, appeared at a rally today at the edge of Sanaa University campus, where students and teachers hugged her and threw roses.
"I thank everyone for supporting me," she told reporters.
A banner held up at the rally read: "We want the facts revealed in the case of Hanan al Samawi" while the crowd chanted: "No to the arrest of students.
A senior Yemeni security official told AFP that only one parcel had been sent by a woman who "impersonated" Hanan al Samawi and put the student's phone number on the receipt. The second package was sent by a man, he added.
A Yemeni official said Ms Samawi, 22, was freed on condition she present herself for further questioning if required.
Hundreds of students had rallied at Sana'a University on Sunday calling for her release.
Yemeni authorities arrested more suspects today while they released some employees from the Sanaa offices of FedEx and UPS, the courier firms reportedly used for the parcels, a security official said.
Yemeni officials have said they were examining 26 other seized packages and overhauling their security system on cargo.
Meanwhile a team of US investigators is headed to Yemen to help search for suspects, as an alleged Saudi bombmaker was named as a key suspect in the failed plot.
A US official in Washington said Ibrahim Hassan al Asiri, a 28-year-old alleged al Qa'eda bombmaker, had emerged as a "leading suspect" in the parcel bomb plot uncovered late on Thursday.
"Al Asiri's past activities and explosives' experience make him a leading suspect," the official said.
Al Asiri, thought to be hiding in Yemen, is wanted for a string of high-profile attacks linked to al Qa'eda in the Arabian Peninsula (AQAP), the Yemen-based branch of Osama bin Laden's network.
The US official said: "There are indications he may have had a role in past AQAP plots, including the attempted assassination of a Saudi official and last year's failed Christmas Day attack."
The White House's top counter-terrorism official, deputy national security adviser John Brennan, also linked the attempted Christmas Day bombing and the package plot, both of which involved the high explosive PETN.
Evidence suggested the same person built the intercepted parcel bombs and the device worn by the "underwear" bomber, Umar Farouk Abdulmutallab, who botched an attack on a flight to Detroit on Christmas Day 2009, he said.
"I think the indications are right now based on the forensics analysis that it's an individual who has been responsible for putting these devices together, the same," he told ABC News yesterday.
"He's a very dangerous individual, clearly somebody who has a fair amount of training and experience."
Al Asiri features on most-wanted terror lists in both Yemen and Saudi Arabia. In August 2009 he sent his 23-year-old younger brother on a suicide mission, with 100 grams of PETN underneath his robe, to kill the Saudi intelligence chief, Prince Mohammed bin Nayef, who was wounded but survived.
Yemen today announced a crackdown on cargo shipments, as the state news agency Saba said the country's national committee for civil aviation security has decided "to implement exceptional security measures on all cargo leaving Yemeni airports to ensure the safety of civil aviation."
The committee had also decided to tighten general security at all Yemeni airports, to counteract "methods used by terror organisations", Saba said.
Qatar Airways said on Sunday that a package containing explosives was flown from Sanaa to Doha and then on to Dubai on one of its aircraft. A source said that the plane was a passenger flight.
The bomb had the explosive PETN hidden inside a computer printer with a circuit board and mobile phone SIM card attached, officials said.
The second parcel found at East Midlands airport in the UK apparently travelled through Cologne in Germany. The British prime minister, David Cameron, said it appeared designed to blow up a plane.
Shortly after the discovery of the bombs, Britain banned all freight from Yemen from coming into the country, including in transit. On Saturday, Germany and France took similar measures to suspend air freight from Yemen.
Mr Brennan, led a team of national security and intelligence officials in a second day of meetings assessing the best options in striking back at the al Qa'eda offshoot.
US officials have said the parcel bombs intercepted in Dubai and Britain were addressed to synagogues in Chicago.
On October 11, AQAP's military leader, Qassim al Rimi announced that his group has "men doing work 'internationally'," the US monitoring group SITE reported.
Al Rimi said: "We will not experience war in our countries while our enemies are safe in their countries,"
The incident is seen as an opportunity for the White House to persuade Yemen to widen its war on terror by allowing the Americans a more active role.
Yemen's government has worked closely with US counter-terrorist advisers from military special operations units, and Yemen's president acknowledged on Saturday that his government is working with the CIA, according to a translation of his remarks by Yemen's embassy in Washington.
But President Saleh has been reluctant to allow expanded use of armed drones or regular raids by US special operations units on Yemeni soil, for fear of being accused of being labelled an American stooge by the militants or his own people.
The mail bomb plot could pressure him to reconsider, according to Chris Boucek, a Yemen expert with the Carnegie Endowment for International Peace.
"The next attack, if something actually blows up, the US won't be able to be so restrained," he said.
The danger, Mr Boucek said, is that the US might overreact and push Yemen to accept participation so overt that it undercuts Yemen's perceived legitimacy.
The Obama administration launched a clandestine war against Yemen's al Qa'eda branch just months after President Barack Obama took office, and stepped up the tempo in the aftermath of the Christmas attack and AQAP's growing role in other plots against the US. That war has been waged mostly in secret, at the demand of Mr Saleh's government.
Yemeni government ministers did, however, acknowledge publicly that the US carried out cruise missile strikes last December against al Qa'eda targets.
While Yemeni officials have complained bitterly about collateral damage from some of the attacks, US administration officials insist that the Yemeni government has signed off on those missions at the highest level, as part of combined counter-terrorist operations.
Those operations are coordinated from an intelligence command centre the US runs with the Yemenis, where it shares intelligence gathered by satellite, manned aircraft and unmanned drones, some of which were observed last week, as reported in the Yemeni press.
Building on that, the White House could push for more unilateral clandestine missions on Yemeni soil as well as an increased operational tempo against the militants, as the US has done against Taliban and al Qa'eda targets in Afghanistan and Pakistan.
The administration could also ask to fly Predator and Reaper drones from inside Yemen, something Yemeni officials say they have already requested. Currently, drones and other observation platforms must be based off US ships or fly from other US air bases in the region, limiting the amount of fuel they have left by the time they reach a target or observation point. Some of those drones are overseen by the Pentagon's special operating units, others by the CIA, depending on the given mission.
Mr Boucek said the hard part will be finding targets to hit. Over the past few months, Yemeni forces swept through many of the areas where al Qa'eda holds sway, but Mr Boucek said the operations netted only a few viable suspects.
White House officials are quick to point out that the counter-terrorist operations only comprise one part of their aid to Yemen. The US has expanded military and economic aid to augment the counter-terrorist programme, in what it calls a "whole of government" approach. Senior administration officials said the economic aid, along with working with the Yemeni government to improve its human rights record and provide better services to its people, is designed to dry up the roots of the conflict.
The US will provide some $300 million in military, humanitarian and development aid to Yemen this year, according to the State Department counter-terrorism coordinator, Daniel Benjamin. About half of that is for military equipment and training, including some 50 special-operations trainers for Yemeni counter-terror teams.