The stepped-up assistance comes as two weeks of air strikes by Saudi Arabia and its Gulf Arab allies have largely failed to halt advances by the Iran-backed Houthi forces.
The US officials said the expanded assistance includes intelligence data that will allow the Saudis to better review targets.
“We have opened up the aperture a bit wider with what we are sharing with our Saudi partners,” said one US official.
“We are helping them get a better sense of the battlefield and the state of play with the Houthi forces. We are also helping identify ‘no strike’ areas they should avoid” to minimise any civilian casualties, the official said.
On Saturday, the Red Cross delivered a second planeload of aid to Yemen in as many days.
The aid is urgently needed for hundreds wounded in fighting between pro-government forces and the Houthis, who are allied to troops loyal to ex-president Ali Abdullah Saleh.
Coalition warplanes on Saturday launched at least 11 raids around Sanhane, hometown of Mr Saleh south-west of Sanaa, and a camp of special forces loyal to the ex-strongman, witnesses said.
The strikes came after fierce clashes in South Yemen killed at least 25 people overnight, and air raids against Houthi positions in Aden, Yemen’s second city.
US ally Saudi Arabia is concerned that the violence could spill over the border it shares with Yemen, and is also worried about the influence of Shiiite Iran, which has denied Saudi allegations it has provided direct military support to the Houthis.
Local militiamen in Aden said they captured two Iranian military officers advising Houthi rebels, during fighting on Friday evening.
If confirmed, the presence of two Iranian officers, whom the local militiamen said were from an elite unit of Iran’s Revolutionary Guards, would deepen tensions between Tehran and Riyadh.
The US, whose fight against Al Qaeda militants in Yemen has been dealt a heavy setback by the Houthi takeover of the capital Sanaa and ousting of the previous government, has avoided a direct role in the worsening conflict. It will still stop short of picking targets for the Saudis.
But Washington has come under pressure to do more to assist the alliance led by Saudi Arabia, which fears the Houthi advance is expanding the influence of arch foe Iran to its border.
Saudi concerns of growing Iranian influence have also been heightened by nuclear talks between Tehran and world powers that could result in a deal by June 30 removing punishing sanctions on the country.
A senior US diplomat said earlier this week that Washington was speeding up arms supplies and bolstering intelligence sharing with the Saudi-led alliance. The Pentagon has said it is beginning aerial refuelling of Arab coalition jets — although outside Yemeni airspace.
Until recent days, US intelligence support was limited to examining Saudi targeting information to try to affirm its accuracy.
The US role has now expanded in size and scope, involving more detailed “vetting” of targeting information prepared by the Saudis, with a particular interest in helping the Saudis to avoid civilian casualties.
“The United States is providing our partners with necessary and timely intelligence to defend Saudi Arabia and respond to other efforts to support the legitimate government of Yemen,” said Alistair Baskey, a White House spokesman.
The Saudi-led air campaign is aimed at rolling back territorial gains by the Houthis and reinstalling Yemeni president Abdrabu Mansur Hadi, who has fled the country.
While the White House announced US intelligence support soon after the operation began, US officials said that data sharing had been extremely minimal in the campaign’s early days. That is partly due to legal barriers, the officials said.
While the US has used lethal force against an Al Qaeda offshoot in Yemen, it does not consider itself at war with the Houthis. Some officials said the US administration’s analysis is that it lacks the ability under international and US law to collaborate with the Saudis in an offensive against the Houthis.
Mr Baskey said that US actions were “fully consistent with applicable domestic and international legal requirements.”
Deputy secretary of state Antony Blinken spoke in general terms about the expanded cooperation during a Monday visit to Riyadh.
“Saudi Arabia is sending a strong message to the Houthis and their allies that they cannot overrun Yemen by force,” Mr Blinken said.
“As part of that effort, we have expedited weapons deliveries, we have increased our intelligence sharing, and we have established a joint coordination planning cell in the Saudi operation centre,” he added.
The US has sent a 20-member military coordination team to interact with the Gulf allies, led by Marine Major General Carl Mundy.
The US this week started daily air-to-air refuelling flights of fighter jets from Saudi Arabia and the UAE.
But even with its refuelling flights, the US is exhibiting caution — carrying out the flights outside Yemeni airspace and requesting financial reimbursement from allies.
* Reuters, Agence France-Presse
