Policemen try to separate anti-government protesters (back to the camera) from supporters of Yemen's President Ali Abdullah Saleh in the southern city of Taiz April 23, 2011. [Photo/Agencies]

SANAA, Yemen - Yemen's embattled president agreed Saturday to a proposal by Gulf Arab mediators to step down within 30 days and hand power to his deputy in exchange for immunity from prosecution, a major about-face for the leader who has ruled for 32 years.

A coalition of seven opposition parties said they also accepted the deal but with reservations. Even if the differences are overcome, those parties do not speak for all of the hundreds of thousands of protesters seeking President Ali Abdullah Saleh's ouster, and signs were already emerging that a deal on those terms would not end confrontations in the streets.

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A day earlier, protesters staged the largest of two months of demonstrations, filling a five-lane boulevard across the capital with a sea of hundreds of thousands of people. Day after day of protest have presented a stunning display of defiance in the face of a crackdown that has included sniper attacks and killed more than 130 people.

The uprising and a wave of defections by allies, including several top military commanders, have left Saleh clinging to power and now appear to be pushing him to compromise on his earlier refusal to leave office before his term ends in 2013.

For decades the former military officer has fended off numerous challenges, deftly maneuvering among the nation's powerful and fractious tribes and using security forces to put down opponents. Al-Qaida's most active franchise has attacked his forces, an armed rebellion has battered the north of the country and a secessionist movement has reappeared in the once-independent south.

At the same time, the country is rapidly running out of water and oil and is the poorest in the Arab world.

The United States has watched the uprising with particular concern because Saleh has been an ally in fighting al-Qaida in the Arabian Peninsula, which is based in Yemen's remote mountainous south and has made several nearly successful attempts to attack US and other targets abroad.

US State Department spokesman Mark Toner said Washington welcomes the proposal for ending the crisis and called for immediate dialogue by all sides on a transfer of power.

"We will not speculate about the choices the Yemeni people will make or the results of their political dialogue," he said. "It is ultimately for the people of Yemen to decide how their country is governed."

Later, the White House in a statement urged all parties in Yemen "to move swiftly to implement" a deal transferring power.

Yemen's President Ali Abdullah Saleh attends a rally in Sanaa in this April 22, 2011 file photo. [Photo/Agencies]