President Obama is welcoming British Prime Minister David Cameron to the White House for talks on subjects ranging from Syria's civil war to preparations for a coming summit of the world's leading industrial nations in Northern Ireland.
Iran, the Mideast peace process, counterterrorism and trade are other likely topics for Monday's meeting.
The U.S. and Russia agreed last week to arrange an international conference to bring representatives of the government of Syrian President Bashar Assad and the opposition to the negotiating table. There is no date yet, but such talks would focus on setting up a transitional government.
Cameron said after a meeting last week with Russian President Vladimir Putin that they both agreed that "we must help drive this process."
The British leader also said Britain, the U.S., Russia and other countries should take part in setting up a transitional government.
Separately last week, the Obama administration announced it will provide $100 million in new aid to Syria, strictly for humanitarian relief for Syrian refugees and not linked to any possible decision on arming the rebels who seek to topple Assad from power.
Total U.S. humanitarian assistance in the war, now in its third year, will surpass $500 million.
The Obama administration has said it is considering providing weapons to vetted units in the armed opposition, among other military options, following the recent revelation of a U.S. intelligence assessment that suggested chemical weapons use by the Assad regime.
Obama has said use of such weapons would cross a "red line."
The president and Cameron also will review priorities for the Group of Eight summit. Cameron will preside over the June 17-18 gathering in Lough Erne, Northern Ireland. The White House said Friday that Obama would stop in Belfast, the capital of Northern Ireland, before joining the summit.
The visit will be Obama's first to Northern Ireland.