The United States has started daily aerial refueling for warplanes in the Saudi-led coalition carrying out air strikes in Yemen, the Pentagon said Wednesday.

The first refueling flight took place on Tuesday night with a US Air Force KC-135 Stratotanker providing fuel for a F-15 fighter jet operated by Saudi Arabia and an F-16 flown by the United Arab Emirates, spokesman Colonel Steven Warren told reporters.

"We will have a tanker sortie every day," Warren said, adding that all flights will be outside of Yemeni air space.

Pentagon had announced plans for aerial refueling earlier and officials say American forces stand ready to fly early warning radar aircraft if necessary.

The move signaled an expanding role for the US military as Washington said Tuesday it was stepping up intelligence sharing with the coalition and expediting the delivery of precision-guided bombs to the Saudis and their Gulf allies.

But US officials and military officers insisted the American assistance was "limited" and would not escalate with aircraft taking part in any bombing raids in Yemen.

President Barack Obama approved intelligence and logistics support for the Saudi-led coalition after Riyadh announced its armed intervention in Yemen against Iranian-backed rebels.

About 12 US military troops are working with the Saudis at a "joint fusion center" in Riyadh, led by a two-star US Marine Corps general, officials said.

US forces, including a helicopter, helped rescue two Saudi pilots on March 26 from the Gulf of Aden after their F-15 fighter suffered engine trouble.

Huthi rebels have seized control of large parts of Yemen including the capital Sanaa and joined forces with security forces who have remained loyal to longtime strongman Ali Abdullah Saleh, forced from power in 2012 after a year-long, Arab Spring-inspired uprising.

Riyadh accuses Tehran of backing the rebels and has vowed to bomb them into submission to prevent them establishing a pro-Iran state on its doorstep.