WASHINGTON - President Obama faces a fresh test today of his determination to steer clear of the civil war in Syria when he considers a desperate plea from a longtime U.S. ally.

Turkish Prime Minister Recep Tayyip Erdogan is expected to urge Obama in a White House meeting to move more aggressively to end a conflict that has sent more than 1 million refugees fleeing across Syria's borders and threatens to destabilize the region.

"Syria will be our main topic. … We will draw a road map," Erdogan told reporters before leaving Ankara, Turkey's capital. He said he is bringing evidence of Syrian chemical weapons use to help strengthen his case.

Obama, who has cultivated Erdogan as America's special ally in the Muslim Mideast, appears unlikely to offer more than humanitarian relief. The White House is wary of using the U.S. military to stop Syrian aircraft near the Turkish border by imposing a no-fly zone or taking other direct military action.

The administration also has decided not to arm the Syrian rebels for now, although the policy remains under review.

With 400,000 Syrian refugees on Turkish soil and protests against Erdogan's support for the Syrian insurgents, the prime minister is under strong domestic pressure to get Obama's help during his one-day visit to Washington.

Several of Syria's other neighbors also are urging the White House to assume a greater role in pushing President Bashar Assad's government out of power.

Qatar and Saudi Arabia want Washington to arm and protect the rebels, while Jordan and Lebanon are seeking relief for the 500,000 refugees that each is hosting within its borders. Israel wants the Pentagon to help safeguard the vast chemical-weapons infrastructure and arsenal in Syria.

Bulent Aliriza, director of the Turkey Project at the nonpartisan Center for Strategic and International Studies in Washington, said Ankara and Washington both seek to force Assad out. He said Erdogan is frustrated that "while Turkey has been accelerating toward that goal, the U.S. has been hitting the brakes."

Turkish officials say they aren't pushing for a particular military action, but for the U.S. to persuade Assad to negotiate a transition to a new government.

Syria rebels, regime troops fight in Aleppo prison / A14