WASHINGTON -- When President Barack Obama meets over the next month with leaders from Mideast and other regional nations, he will have a timely opportunity to try to rally the Syrian opposition's main backers around a unified strategy to oust Syrian President Bashar Assad.

Jordan, Turkey, Qatar and the United Arab Emirates - whose Sunni Muslim leaders will meet separately with Obama starting April 16- are all believed to be arming or training rebel forces seeking to overthrow Assad's regime. But disparate political, geographic and religious considerations have led to conflicting approaches to which rebel factions to back and what kind of support to provide.

Infighting among mostly Sunni opposition groups and their failure to agree on a power structure to take over if Assad falls has been an important factor aiding the Alawite president as he clings to power two years into a civil war that has left at least 70,000 dead. Alawites are an offshoot of Shiite Islam, and the civil war has largely broken down along sectarian lines.

As resolute as Obama and most U.S. allies are that Assad must go, officials are increasingly worried about what Syria will look like if the regime falls before opposition groups can agree on a governing structure. That has resulted in extra U.S. pressure on regional allies to convince the opposition to unite.

White House spokesman Jay Carney said the high-level visits by leaders from the four nations reflect Obama's "deep personal interest" in the region and his commitment to the policies the U.S. is advocating.

"He will use these opportunities to discuss the complex developments in the broader Middle East," Carney said. "Not just Syria, but including Syria."

He pointed to other developments related to the Arab Spring and Obama's visit in March to Jordan, Israel and the Palestinian territories as other topics the president would likely discuss with the Arab leaders. Secretary of State John Kerry also is returning to the Middle East on Saturday for meetings on Syria and Israeli-Palestinian peace.

Additionally, senior Obama administration leaders at the White House, State Department and Pentagon held a high-level meeting Friday that focused on Syria among its top national security priorities, according to two officials familiar with the discussion who spoke on condition of anonymity because they were not authorized to disclose the talks to the news media. Senior U.S. officials have been meeting regularly to discuss a range of options on U.S. involvement in Syria, including whether to arm the rebels.

"We are constantly reviewing every possible option that could help end the violence and accelerate a political transition," said Caitlin Hayden, a spokeswoman for the National Security Council. "We are focusing our efforts on helping the opposition become stronger, more cohesive and more organized."

The global community's response to Syria will also be high on the agenda next Thursday, when Obama meets with U.N. Secretary-General Ban Ki-moon in the Oval Office. Washington has resisted arming the rebels, in part for fear that some weapons could fall into the hands of jihadi groups that are designated as terrorist fronts linked to al-Qaida.

But the U.S. has helped train some of the opposition fighters - mostly former Syrian regime soldiers who have defected - in Jordan and tacitly endorsed shipments of arms to the opposition from Qatar, Turkey and Saudi Arabia.

Additionally, Kerry said last month that the U.S. will not stop Western nations seeking to open the possibility of arming the rebels, including Great Britain and France.

But the bulk of the aid to rebels has come from Sunni-led governments in Turkey and the Mideast - as several Shiite leaders in the regions have spirited weapons, fighters and aid to Assad's forces.

Turkey and Qatar, along with Saudi Arabia, are widely believed to have been providing rebels with tanks and surface-to-air missiles to fight regime soldiers. Salman Shaikh, a Mideast expert who specializes in Gulf politics, said those countries have strongly backed the opposition Syrian National Council and its allied fighters - which include elements of the Muslim Brotherhood and Islamists, as well as secular groups.

The United Arab Emirates, by contrast, has been unenthusiastic about aiding Islamist elements of the opposition. Shaikh said the Emirates is believed to be sending limited weapons, like small firearms and ammunition, to secular fighters but mostly have focused on supplying the opposition with humanitarian aid.

Syria's protracted civil war has been particularly taxing for Jordan, a close U.S. ally that shared its northern border with Syria and has absorbed more than 460,000 refugees fleeing the conflict - the equivalent of 10 percent of Jordan's population. It's been just a few weeks since a meeting between Obama and Jordan's ruler, King Abdullah II, in which Syria topped the agenda.

"We are extremely concerned of the risk of prolonged sectarian conflict that, if it continues as we're seeing, leads to the fragmentation of Syria," Abdullah said then, standing alongside Obama in Amman.

Jordan mostly has been helping train and arm rebel fighters who defected from Assad's forces and has done so with U.S. help. It also has served as a way station for rebels' weapons flow into Syria, and this week drew a harsh warning from Assad about "playing with fire" amid Jordanian fears that its larger neighbor might try to retaliate.

The two leaders will meet in Washington on April 26 in what one U.S. diplomat predicted will be Abdullah's attempt to ensure that he has full U.S. backing as Jordan's campaign to help the rebels continues. The diplomat spoke on condition of anonymity to discuss the talks more candidly.

"Regional players will find it difficult to always be singing off the same sheet," said Shaikh, director of the Brookings Doha Center think tank in Doha. "The U.S. hanging back and outsourcing a regional role is never going to achieve the goal of a unified opposition (to the regime) or even the military on the ground."

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Associated Press writer Lolita C. Baldor contributed to this report.

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