Syrian government helicopters attacked a village in northwestern Syria with chemical weapons, killing at least six people and injuring scores, activists and opposition groups said. (Reuters)

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 alleged 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 alleged attack 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 toxins.

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.”

A man inspects a site targeted in what activists said was a poison gas attack in the Syrian village of Sarmin in Idlib province on March 17, 2015. (Mohamad Bayoush /Reuters)

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

[Graphic: A bird’s-eye view of war-torn Syria]

Amateur video of the alleged aftermath shows three dead infants wrapped in white sheets, with foam at 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 receiving treatment at a medical facility, some of them breathing through what appear to be oxygen masks.

The alleged attack coincided with a meeting Monday in Switzerland between U.S. Secretary of State John F. Kerry and Iranian Foreign Minister Mohammad Javad Zarif that focused on negotiations over Iran’s nuclear program. Iran is a chief Assad ally.

On Sunday, 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.

Critics of Assad fear that 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 Adolf Hitler.

[Read: U.S. looks into new Syria chemical weapons attack claims]

Meanwhile, a report released Tuesday by Amnesty International accuses the Assad regime of carrying out attacks in November on the eastern city of Raqqa, the de facto capital of the Islamic State militant group, that may amount to war crimes. As many as 115 civilians were killed in the alleged attacks, which the report called “unlawful.”

The Islamic State, also known as ISIS or ISIL, is an enemy of the Syrian government but also an international threat. Many of those opposed to Assad 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’s, that allowed the United Nations and the Organization for the Prohibition of Chemical Weapons to dismantle Syria’s chemical weapons stockpiles.

Reports surfaced during the dismantling process of continued attacks involving chemical agents. In a September 2014 report, the OPCW said it found “compelling evidence” that toxins had been “systematically and repeatedly” used that year.

The alleged attack on Monday coincided with the 27th anniversary of a chemical weapons assault on the Kurdish town of Halabja by the warplanes of Iraqi dictator Saddam Hussein. About 5,000 people were killed in that attack.