President Barack Obama has authorized sending weapons to Syrian rebels for the first time, U.S. officials said Thursday, after the White House disclosed that the United States has conclusive evidence Syrian President Bashar Assad’s government has used chemical weapons against opposition forces trying to overthrow him.

Obama has repeatedly said the use of chemical weapons would cross a “red line” that would trigger greater American intervention in the two-year crisis.

Sen. John McCain, R-Ariz., one of the strongest proponents of U.S. military action in Syria, said he was told Thursday that Obama had decided to “arm the rebels”, a decision confirmed by three U.S. officials. However, the officials cautioned that no decisions had been made on the specific type of weaponry or when it would reach the Syrian rebels, who are under increasing assault from Assad’s forces.

“This is going to be different in both scope and scale in terms of what we are providing,” said Ben Rhodes, Obama’s deputy national security adviser.

The U.S. has so far provided the Syrian rebel army with rations and medical supplies.

Thursday’s announcement followed meetings at the White House this week that revealed divisions within the administration over U.S. involvement in Syria’s civil war.

The proponents of more aggressive action — including Secretary of State John Kerry — appeared to have won out over those wary of sending weapons and ammunition into a war zone where Hezbollah and Iranian fighters are backing Assad’s armed forces, while extremists backed by al-Qaida extremists support the rebellion.

Obama still opposes putting American troops on the ground in Syria and the U.S. has made no decision on operating a no-fly zone over Syria, Rhodes said.

U.S. officials said the administration could provide the rebels with a range of weapons, including small arms, ammunition, assault rifles and a variety of anti-tank weaponry such as shoulder-fired remote-propelled grenades and other missiles.

All of the officials insisted on anonymity in order to discuss internal administration discussions.

Word of the stepped-up assistance followed new U.S. intelligence assessments showing that Assad has used chemical weapons, including sarin, on a small scale multiple times in the last year.

Up to 150 people have been killed in those attacks, the White House said. In a report Thursday, the United Nations said that nearly 93,000 people have been killed in Syria over the last two years.

The White House said it believes Assad’s regime still maintains control of Syria’s chemical weapons and does not see any evidence that rebel forces have launched attacks using the deadly agents.

The Obama administration announced in April that it had “varying degrees of confidence” that sarin had been used in Syria. But they said at the time that they had not been able to determine who was responsible for deploying the gas.

Obama has said repeatedly that the use of chemical weapons would cross a “red line” and constitute a “game changer” for U.S. policy on Syria, which until now has focused on providing the opposition with nonlethal assistance and humanitarian aid.

The White House said it had notified Congress, the United Nations and key international allies about the new U.S. chemical weapons determination. Obama will discuss the assessments, along with broader problems in Syria, next week during the G-8 summit in Northern Ireland.

Among those in attendance will be Russian President Vladimir Putin, Assad’s most powerful backer. Obama and Putin will hold a meeting on the sidelines of the summit, where the U.S. leader is expected to press his Russian counterpart to drop his political and military support for the Syrian government.

“We believe that Russia and all members of the international community should be concerned about the use of chemical weapons,” Rhodes said.

The U.S. has so far provided the Syrian rebel army with rations and medical supplies. In April, Kerry announced that the administration had agreed in principle to expand its military support to the opposition to include defensive items such as night vision goggles, body armor and armored vehicles.

The Syrian fighters have been clamoring for bolder Western intervention, particularly since an estimated 5,000 Hezbollah guerrillas are now propping up Assad’s forces. Assad’s military success last week at Qusair, near the Lebanese border, and preparations for offensives against Homs and Aleppo have made the matter more urgent.

While McCain has pressed for a greater role for the U.S. military, other lawmakers have expressed reservations about American involvement in another conflict and fears that weapons sent to the rebels could fall into the hands of al-Qaida-linked groups.

Sen. Chris Murphy, D-Conn., a member of the Senate Foreign Relations Committee, condemned the Assad regime but expressed serious concerns about the United States being pulled into a proxy war.

“There are many actions that the United States can take to increase our humanitarian assistance to refugee populations and opposition groups short of injecting more weapons into the conflict,” Murphy said. “I urge the president to exercise restraint and to consult closely with Congress before undertaking any course of action to commit American military resources to Syrian opposition forces.”

House Speaker John Boehner, R-Ohio, also urged the White House to consult with Congress.

“It is long past time to bring the Assad regime’s bloodshed in Syria to an end,” he said through a spokesman, Brendan Buck. “As President Obama examines his options, it is our hope he will properly consult with Congress before taking any action.”