The Syrian civil war has become an “incubator of extremism” and a "magnet" for foreign fighters, and poses growing risks to US interests and allies, US officials told frustrated lawmakers Thursday. The three year old conflict is also likely to go on for a long time, they assessed, as it pulls in foreign fighters from both sides of the Sunni-Shia sectarian divide, and both Bashar al-Assad and his opponents believe they can win.

“The hard reality is that the grinding Syrian civil war is now an incubator of extremism, on both sides of the sectarian divide.” Deputy Secretary of State William Burns told the Senate Foreign Relations Committee Thursday, at a hearing on the Syrian civil war that led off with the deepening US-Russian rift over Ukraine.

“We face a number of serious risks to our interests as a result,” Burns said. “The risk to the homeland from global jihadist groups…the risk to the stability of our regional partners….and the risk to the Syrian people, whose suffering constitutes the greatest humanitarian crisis of this new century.”

That grim assessment may portend the US deepening its support for Syrian opposition fighters now battling both Al Qaeda-linked groups and Assad, and stepped up US counter-terrorism efforts, in coordination with regional partners and European allies alarmed by the threat posed by jihadi fighters returning from Syria.