BEIRUT, Lebanon - Syrian government helicopters attacked a village in northwestern Syria with chlorine gas, killing at least six people and wounding scores, activists and opposition groups said Tuesday.

The attack occurred overnight Monday in Sarmin, in Idlib province, according to the Local Coordination Committees activist collective and the Britain-based Syrian Observatory for Human Rights.

The incident follows the U.N. Security Council's adoption this month of a resolution condemning the use of chemical weapons in Syria. The U.S.-drafted resolution does not assign blame for previous chemical attacks in Syria but warns of military intervention in the event of further use of toxics.

Salem al-Meslet, a spokesman for the Syrian Opposition Coalition, said in a statement that at least six people were killed and scores injured, including toddlers, in the attack.

Meslet called for U.N. action, saying: "Enough is enough. [President Bashar al-Assad] knows he can get away with murder."

An unidentified Syrian government official denied responsibility for the attack, blaming it on rebels, the Associated Press reported.

Amateur video of the alleged aftermath shows three dead infants wrapped in white sheets, foam oozing from their mouths and noses. In the video, which could not be independently verified, a man is heard blaming the "criminal" Assad regime.

Another video purports to show victims getting treatment at a medical facility, some of them breathing through apparent oxygen masks.

On Sunday, Secretary of State John Kerry stirred controversy with a television interview in which he appeared to suggest that the United States was willing to negotiate directly with the Syrian leader. Afterward, the State Department clarified that the United States would not engage directly with Assad.

Assad critics fear the Obama administration is softening its opposition to the Syrian leader.

On Tuesday, Prime Minister Ahmet Davutoglu of Turkey - a Washington ally that vehemently opposes the Syrian regime - said in a televised speech that negotiating with Assad would be like shaking hands with Hitler.

Meanwhile, a report released Tuesday by Amnesty International accuses the Assad regime of possible war crimes for attacks in November on the eastern city of Raqqa, the de facto capital of Islamic State extremists. As many as 115 civilians were killed in the attacks, which the report called "unlawful."

The Islamic State is an enemy of the Syrian regime but also an international threat. Many Assad opponents are concerned that the United States is shifting its focus away from ousting him to defeating the Islamic State.

In late 2013, President Obama threatened airstrikes against the Syrian government over its alleged use of chemical weapons.

Those strikes were averted by a deal backed by the United States and Russia, an ally of Assad, that allowed the United Nations and the Organization for the Prohibition of Chemical Weapons to dismantle Syria's chemical-weapons stockpiles.