Britain: Saudis could not accept "Iranian-backed regime in Yemen"

(Adds efforts for a political solution, paragraph 6)

WASHINGTON, March 27 (Reuters) - British Foreign Secretary Philip Hammond said on Friday that Saudi Arabia felt it necessary to intervene in Yemen to avoid Iranian-backed rebels taking over the country along its southern border.

"The Saudis are very exercised by the idea of an Iranian-backed regime in Yemen," he told reporters during a visit to Washington. "They cannot accept the idea of an Iranian-backed regime in control of Yemen, which is why they felt compelled to intervene the way they have."

For a second day Saudi warplanes targeted positions of the Houthi rebels, who control the capital Sanaa and have driven south to threaten the southern port of Aden.

"We know there has been Iranian support for the Houthi and we are all concerned to avoid this becoming a proxy war," he added.

Hammond said he was in Riyadh on Monday when it clear that the Saudis were occupied by the situation in Yemen.

He said efforts were underway to bring the Yemeni sides together to work out a political deal. "I hope that both the Saudis and the Iranians will support those," he added.

Separately, on negotiations for an Iranian nuclear deal, Hammond said of the six areas to cover in the agreement: "We are better than halfway in terms of having numbers of areas where we are close enough that we can be confident that in the end game we'll get through."

"We are hopeful we will be making progress over the next 48 hours," he said.

Tehran is meeting in Lausanne, Switzerland with six major powers: the United States, Britain, France, Germany, Russia and China. They aim to hammer out a preliminary framework for an accord by the end of this month ahead of a full deal by June 30.

Hammond declined to say what the main areas of disagreement were with the Iranians in the talks. However, he added that he is willing to travel to Lausanne to join the talks this weekend if necessary.

The "Iranian negotiating team in Lausanne wants to get a deal. What we of course never quite know is what the internal politics back in Tehran looks like," he added.

He played down public criticism by France of the negotiations, saying some skepticism added a balance to the negotiating process. "I think that is positive and constructive," he said. (Reporting by Lesley Wroughton; editing by David Storey, David Gregorio and Richard Chang)