U.S. finalizing plan to boost support for Syrian rebels: sources

The United States would increase assistance and send the shipments to moderate rebel factions mostly based in Jordan, along Syria's southern border, the officials familiar with the plan told Reuters.

The additional supplies are likely to be modest and will not include surface-to-air missiles, the officials said, raising questions over the impact in a civil war that has killed an estimated 136,000 people, produced nine million refugees and threatens to destabilize the region.

Rebels have urged the Obama administration to provide advanced weapons including surface-to-air missiles and exert greater military pressure on Russia-backed Syrian President Bashar al-Assad, who has intensified bombings of rebel neighborhoods in recent month.

But the United States fears supplies of advanced weapons to pro-Western rebels could be diverted to Islamic militant groups, who could use them to attack allied, Israeli or civilian aircraft, the U.S. officials said, explaining why the surface-to-air missiles won't be included in the assistance.

President Barack Obama has resisted becoming entangled in Syria's complex, two-year civil war, but has faced criticism for failing to take a tougher stand given the immensity of the humanitarian crisis.

QUESTIONS OVER U.S. ROLE

Details of how much aid will flow to the screened rebel groups are the subject of continuing discussions. It's also unclear, for instance, how much would be covert or whether there would be a U.S. military or special forces role.

U.S. allies, including Saudi Arabia and Qatar, have provided weaponry to various rebel factions during the conflict, including some Islamist groups now at odds with moderate rebels grouped under the umbrella of the Free Syrian Army.

The assistance does not require additional funding from Congress, said the officials, who declined to be identified because they are not authorized to speak with the media.

"Now we have to finalize the plans," one official said.

National Security Council spokeswoman Caitlin Hayden declined to comment.

A former government official familiar with the plan said that training would be done in small tranches and that U.S. allies, including Saudi Arabia, Jordan, the United Arab Emirates and France, are likely to participate.

The sources said that while the Obama administration accepts that the plan will not turn the tide of the conflict decisively against Assad, the U.S. assistance could improve the chances that if Assad is deposed the United States will have allies among successful revolutionary forces.

U.S. and European officials say the most powerful anti-Assad factions are militant groups such as the Al-Nusrah and the Islamic State of Iraq and the Levant, some of which either have links to Al Qaeda or are so extreme that even Al Qaeda has denounced them.

The more militant Islamist rebel factions already control swathes of territory in Syria's northeast and along its border with Iraq, according to American officials. Reuters