Republicans blame Obama as Saudi Arabia bombs Yemen rebels

US Republicans warned Thursday that Saudi-led air-strikes in Yemen, apparently conducted without US coordination, show Arab allies have lost trust in the Obama administration as it navigates delicate nuclear talks with Iran.

As warplanes from Saudi Arabia and other allies pounded Huthi Shiite rebel positions for a second straight day, hawkish US lawmakers expressed alarm at the "proxy war" unfolding in the Middle East, and pinned part of the blame on President Barack Obama's foreign policy.

The Saudi-led intervention without notifying Washington ahead of time "signals a reality that the countries in the region no longer have confidence or are willing to work with the United States of America," Senator John McCain told reporters.

He said he heard "repeatedly from leaders in the region that they believe that we are forming some kind of Faustian bargain with the Iranians, which would then lead to the great danger to those countries."

Washington and other world powers are in the midst of intense negotiations with Tehran over limiting its nuclear program in exchange for a lifting of Western economic sanctions.

Senator Lindsey Graham, who has signalled he may run for president in 2016, accused Obama of softening America's power in the Middle East -- for example by refusing to engage more directly in Syria's civil war -- in order to not disrupt the delicate nuclear negotiations with Iran.

Such action has "led to the rise of (Islamic State group) ISIL, to their flourishing, and now it's leading to a full-scale sectarian war" which could spill over into Syria, Iraq, Libya, Lebanon and Jordan, Graham said.

US engagement has served for decades as a moderating influence in the region, Graham noted.

But "the fact that the Arab coalition no longer trusts us, or feels they need to inform us as what they're about to do, is chilling," he said.

General Lloyd Austin, head of US Central Command, told a Senate hearing that he had little advance notice of the Saudi air strikes launched on Wednesday.

Austin said he was informed by Saudi Arabia about the operation only "shortly before they took action."