The U.N. refugee agency needs money to help overstretched host countries cope. Of the $1 billion in refugee aid pledged at a donor conference in Kuwait in January, only $200 million has come through, officials said.
"We are doing everything we can to help, but the international humanitarian response capacity is dangerously stretched," said the U.N. High Commissioner for Refugees, Antonio Guterres, adding that "Syria is spiraling toward full-scale disaster."
The uprising against Assad began in March 2011 with peaceful protests, but soon became a civil war. The rebel takeover of Raqqa, a city of 500,000, would consolidate opposition gains in the northern towns along the Euphrates River, which runs from Turkey to Iraq.
The Britain-based Syrian Observatory for Human Rights, an activist group, said rebels seized control of the military intelligence headquarters and another security building after three days of fighting with regime holdouts.
In southern Syria, rebel fighters detained about 20 U.N. peacekeepers Wednesday, said U.N. deputy spokesman Eduardo del Buey. The peacekeepers are part of a force that monitors a cease-fire between Israel and Syrian troops on the Golan Heights.
Video circulated by the Observatory claims to show Syrian rebels detaining the peacekeepers in the city of Daraa. The rebels, according to the video, accuse the peacekeepers of assisting the Syrian regime in redeploying in an area near the Golan that the fighters had seized a few days earlier.
Del Buey said the U.N. observers were on a regular supply mission when they were stopped by the rebels. He said a team was dispatched to try to resolve the issue. The Observatory quoted rebels as saying the peacekeepers, all Filipinos, would not be released until regime forces withdraw from a village called Jamla.
The U.N. Security Council demanded their immediate and unconditional release.
In Belgium, the top rebel commander renewed an appeal to the international community to send weapons to the opposition.
Gen. Salim Idris, head of the rebels' Supreme Military Council, asked for anti-tank and anti-aircraft missiles to protect Syrian civilians from Assad's warplanes.
He said Russia and Iran are aiding the regime, while the West, while calling for Assad's ouster, is not doing enough to help the rebels.
"The people don't understand why the international community just looks at the news on their TVs," he said. "They just speak in the media and say, `that is not good and the regime must stop and must go, Bashar must go.' And they don't act."
Britain seemed to be stepping up its support. British Foreign Secretary William Hague said his country would provide armored vehicles, body armor and search-and-rescue equipment to the opposition. But he said Britain is sticking to the European Union's sanctions against Syria, which include an arms embargo.
In Cairo, the 22-member Arab League gave a diplomatic boost to the opposition. The League's chief, Nabil ElAraby, offered Syria's seat to the opposition, provided it forms a representative executive council. The League had suspended Syria's membership in 2011, after Assad's government did not abide by an Arab peace plan.