Sanaa // Tanks were deployed 500 metres from the US embassy in Sanaa yesterday with Yemen's elite special forces posted outside amid fears of a terror attack by Al Qaeda.
Hundreds of additional security forces were deployed at government facilities and western embassies and businesses in the city.
Strict checkpoints were introduced around the embassy and lorries were not allowed anywhere near the main road to the building.
The United States and other western nations have ordered their embassies in Yemen's capital to close today and tomorrow after intelligence reports of an increased risk of attack.
The suspected threat prompted Washington to issue a highly unusual worldwide travel alert on Friday, a day after the US state department announced it was closing 22 US embassies across the Middle East and beyond over the weekend and into this week, including diplomatic missions in the UAE, Saudi Arabia, Yemen, Kuwait and Iraq.
Britain announced the closing of its embassies in Sanaa today and tomorrow and the foreign office has urged British citizens to leave Yemen. Germany and France followed suit yesterday.
The heightened alert came after American intelligence agencies intercepted communications between senior operatives of Al Qaeda in the Arabian Peninsula in which they discussed plans for a terrorist plot.
Yemeni intelligence officials warned the US of unusual chatter among militants in recent weeks that had increased before the weekend.
"The location of these closures seems to suggest the US authorities don't know the specific location, but it is somewhere within the operational area of AQAP," said Frederic Wehrey, an Arabian Gulf security expert at the Carnegie Endowment for International Peace, a Washington-based think tank.
"At a time we're supposed to be signalling our engagement, I'm quite frankly surprised that the closures are so broad.
"From a messaging standpoint it arguably sends a signal that without even attempting an attack, Al Qaeda was able to shut down our embassy operations in a great swath of the Middle East."
US officials said they were particularly concerned about a possible attack on the US embassy in Sanaa by terror groups on Tuesday. The US travel alert warned of potential terrorist attacks until the end of August.
The Al Qaeda threat came as a number of potentially symbolic dates approach. Today is Laylat Al Qadr, the anniversary of two important dates in Islam during Ramadan, and a time when Al Qaeda has threatened and attacked in the past.
Wednesday is also the anniversary of the 1998 Al Qaeda bombings of US embassies in Nairobi and Dar es Salaam.
The Yemeni affiliate is the only Al Qaeda group that has shown the operational ability to plot significant attacks on American targets, and the US has launched dozens of drone strikes against members of the group in Yemen over the past decade.
The latest drone attacks came as the Yemeni president, Abdurabu Mansur Hadi, met Barack Obama in Washington last week for talks about counter-terrorism cooperation between the two countries, as well as the fate of the 86 Yemenis detained by the US at Guantanamo Bay.
During Mr Hadi's four-day visit, US secretary of defence Chuck Hagel thanked the president for his country's counter-terrorism cooperation. The US has spent about US$247 million over the past two years on helping to build up Yemen's security capacity, the state department says.
In a press conference with Mr Obama, Mr Hadi insisted Yemen would continue the fight against Al Qaeda. "Yemen's cooperation with the United States against the Al Qaeda network is in the interest of Yemen before that of the United States," he said.
The three drone strikes in three southern provinces last week killed 13 people, militants as well as civilians, one of them a child. T
he drone strikes are widely condemned by Yemenis because of civilian casualties and the US had scaled back the attacks over the past two months.
That there would be a spate of attacks on the eve of the presidential meeting also suggested that US intelligence officials believed the AQAP threat was imminent.
"Why embarrass a close ally on the eve of a White House visit unless it was absolutely necessary?" said Gregory Johnsen, the author of The Last Refuge: Yemen, Al Qaeda and America's War in Arabia. "Likely, these strikes were an attempt to short circuit any attacks that could be under way."
However, many analysts, as well as Yemeni officials, worry that the Obama administration is relying too heavily on drones as a tactic against Al Qaeda's most potent affiliate and that this may be undermining efforts against the group.
A senior Yemeni intelligence official said the agressive drone campaign triggered the latest security worries.
"Al Qaeda is planning for a major attack in retaliation against the continuous drone strikes on Yemeni lands," said the official. "Yemen is at high risk because of its cooperation with the US drone war."
Mr Wehrey said that the Obama administration had relied too much on drones because addressing the larger underlying problems that fuel militancy was a complex and difficult long-term issue that it would rather avoid.
"Provincial marginalisation, economic issues … how do you compel a country like Yemen to reform itself?" he said. "By comparison the drone strategy is seductively easy but may not be the right one."
During the years since AQAP nearly managed to detonate a suicide bomb on an airliner over Detroit on Christmas Day 2009, drone strikes have increased, and so has the group's support and members, increasing from a few hundred fighters to more than 1,000 now, Mr Johnsen said.
As US officials continue to claim that Al Qaeda-affiliated militant groups are on the decline across the region, there are worrying signs that the turmoil in the post-Arab Spring countries as they try to move towards democracy has given renewed life to Islamist militancy.
"Regionally they are trying to exploit chaos in Egypt in the Sinai, they're looking for operational havens in Libya, in Syria … they have shown a remarkable resilience," Mr Wehrey said.
While AQAP has not launched a major attack in more than a year, political instability could provide the group space, which the new threat may indicate, said AbdulSalam Mohmammed, president of the Abaad Strategic Centre in Sanaa.
"Yes, Al Qaeda is weaker today, but with the current security crisis it is very capable of attacking," he said.
* With additional reporting by Taimur Khan in New York