U.S. intelligence agencies have concluded that Syrian President Bashar Assad’s forces used chemical weapons on a small scale against rebel fighters in Syria’s civil war, the White House said on Thursday, June 13.

The assessment, which followed President Barack Obama’s demand for conclusive proof after U.S. intelligence analysts determined earlier this year that chemical weapons had likely been used, could put pressure on Washington to respond aggressively to the crossing of what Obama himself had called a “red line.”

“Following a deliberative review, our intelligence community assesses that the Assad regime has used chemical weapons, including the nerve agent sarin, on a small scale against the opposition multiple times in the last year,” Ben Rhodes, Obama’s deputy national security adviser, told reporters.

“Our intelligence community has high confidence in that assessment given multiple, independent streams of information,” he said. “The intelligence community estimates that 100 to 150 people have died from detected chemical weapons attacks in Syria to date.”

Meanwhile, the White House said Obama is deciding whether to take new action to help Syria’s rebels, while Assad’s surging forces and their Lebanese Hizbullah allies turned their guns on the north.

Assad’s forces fought near the northern city of Aleppo on June 13 and bombarded the central city of Homs, having seized the initiative by winning the open backing of Hizbullah last month and capturing the strategic town of Qusair last week.

The arrival of thousands of seasoned, Iran-backed Hezbollah fighters to help Assad combat the rebellion has shifted momentum in the two-year-old war.

U.S. and European officials anxious about the rapid change are meeting the commander of the main rebel fighting force, the Free Syrian Army, on Friday in Turkey. FSA chief Salim Idriss is expected to plead urgently for more help.

Obama has come under mounting pressure in recent weeks from allies abroad and politicians at home to take more action to help the rebels as the balance of power tilts towards Assad.

He has so far been more cautious than Britain and France, who have already forced the European Union this month to lift an embargo that had blocked weapons for the rebels.

“The president is reviewing and considering what other options are available to him and to the United States as well as our allies and partners for further and additional steps in Syria, and that process continues,” White House spokesman Jay Carney said.

“As terrible as the situation is in Syria, he has to make decisions when it comes to policy towards Syria that are in the best interests of the United States.”

A member of Syrian rebels holds his weapon as he sits on a sofa in the middle of a street in Deir al-Zor, April 2.

Western governments that months ago predicted Assad would soon fall now believe that support from Tehran and Hizbullah are giving Assad the upper hand. However, they also worry that sending arms to rebel fighters could empower Islamist insurgents who have pledged their loyalty to al-Qaeda.

While Britain and France have yet to announce their own decisions to start arming the rebels, their diplomats have been making the case that the best way to counter both threats is to beef up support for Idriss’s mainstream rebel force.

Strengthening the FSA with money, weapons and ammunition, they argue, would both help combat Assad and also provide a counterweight among the rebels to al-Qaeda-linked groups.

France in particular has developed good relations with Idriss while providing funds and non-lethal support, and seems eager to send him military aid.

Among those whose comments put pressure on Obama to act was one of his Democratic predecessors, Bill Clinton.

“The only question is: now that the Russians, the Iranians and Hezbollah are in there head over heels … should we try to do something to try to slow their gains and rebalance the power so that these rebel groups have a decent chance to prevail,” the ex-president was quoted by newspaper Politico as saying.

Assad’s government says its next move will be to re-capture Aleppo in the north, Syria’s biggest city and commercial hub, which has been divided since last year when advancing rebels seized most of the countryside around it.

Syrian state media have been touting plans for “Northern Storm,” a looming campaign to recapture the rebel-held north.

The United Nations, which raised its death toll for the war so far to 93,000 on Thursday, said it was concerned about the fate of residents if a new offensive is launched.

Assad’s army appears to be massing some troops in its footholds in Aleppo province, particularly in loyalist areas such as the enclaves of Nubel and Zahra, although some opposition activists say the government may be exaggerating the extent of its offensive to intimidate rebel supporters.

The government has also launched an offensive in Homs, one of the last major rebel strongholds in the country’s centre.

“There was a fourth day of escalations today on the besieged neighborhoods of Homs’s old city. Early in the morning there were two air strikes followed by artillery and mortar shelling,” said Jad, an activist from Homs speaking via Skype.

Ahmed al-Ahmed, an activist in Aleppo, said the government’s reinforcements in the north were just a distraction from Homs.

“They’ve turned the world’s attention to watching northern Aleppo and fearing an attack and massacres as happened to our people in Qusair, to get us to forget Homs which is the decisive battle.”

  – Reuters