WASHINGTON - The United States is considering extending support to thousands of Syrian rebel fighters, possibly with arms and air strikes, to help them push Islamic State from a strategic pocket of Syrian territory along the Turkish border, US officials say.US backing for the plan would come as moderate rebels in Syria, some trained and backed by the United States, say they have been targeted by Russian air strikes, raising tensions between Washington and Moscow.A decision, the officials said, would likely be made as part of a comprehensive overhaul of the US military's support for rebels to fight Islamic State following setbacks that have all but killed a "train-and-equip" program. The proposal under consideration is for the United States and Turkey to support an amalgamation of largely Arab fighters and would include members of multiple ethnic groups, US officials say.Turkey, wary of Kurdish aspirations to create an independent state, does not want to see Kurdish forces control more of the Syrian side of their border.The fighters, who were proposed by Turkey, include some who have received US vetting, the officials say. Its unclear how many Syrian fighters have received US vetting, although the military acknowledges reviewing upwards of 8,000 potential recruits, many of whom were deemed ineligible for training."We don't have a problem with that (Turkish selection)," said one US military official, speaking to Reuters on condition of anonymity, and cautioning that the matter was still under review by the Obama administration. The official and others interviewed by Reuters declined to name the groups, which in Syria often have competing interests. Two US officials said the fighters numbered in the thousands but declined to offer a precise figure.The aim of the operation would be to push Islamic State forces from a 90-km (56-mile) stretch of Syria's northern border running east toward the Syrian city of Jarabulus, about 130 km northwest of the Islamic State's declared capital of Raqqa. The area is west of the Euphrates river that dissects the Syria-Turkey border.STRATEGIC VALUEChris Kozak, a Syria analyst at the Washington-based Institute for the Study of War, said the territory was strategically valuable to Islamic State, serving as its last significant point of access to the northern border with Turkey.US assistance could include everything from air strikes, to offering equipment and even arms, if approved, the military official said, adding that the different levels of US knowledge about the fighters has added complexity to the review.Turkey and the United States agreed to take the territory in July as part of an agreement under which Ankara allowed the United States to use its bases for strikes against Islamic State. Turkey also started carrying out air strikes on Islamic State targets in Syria.But US officials acknowledged after the agreement was struck that they had not agreed on which Syrian rebels they would support in that zone. That issue has been resolved at a preliminary level, the officials said.Obama has sought to limit direct US military involvement in Syria's civil war to waging air strikes against Islamic State, while training and supporting Syrian rebels fighting them. The US administration, which is seeking to avoid a proxy war with Russia, has so far signaled no intention to protect Syrian rebels from Russian bombing.At a news conference on Friday, Obama acknowledged that the US military's train and equip program had not achieved its goals but said he would continue to work with Syria's moderate opposition."We are going to continue to go after ISIL. We are going to continue to reach out to a moderate opposition. We reject Russia's theory that everybody opposed to Assad is a terrorist," Obama said.US officials have told Reuters that a review is underway that could also result in scaling back and reenvisioning Washington's struggling program to train and equip moderate rebels. About 80 graduates are deployed in Syria now and dozens are still in US training, but the Pentagon has stopped drawing recruits from the Syrian battlefield during the review.At the same time, the Obama administration is weighing the possibility of supporting another, separate rebel push east of the Euphrates river that includes largely Kurdish forces, the military official said.That group, known as the Syrian Arab Coalition, would push south toward Raqqa, the official said.