The State Department said Monday that it is investigating allegations that the Syrian government used a toxic chemical in an attack on a rebel-controlled area, raising questions about whether President Bashar al-
Assad is violating an international agreement to destroy his most lethal chemical stockpiles.

“We have indications of the use of a toxic industrial chemical, probably chlorine, in Syria this month,” State Department spokeswoman Jen Psaki said. She said the toxin was used in the rebel-held village of Kafr Zeita, in Hama province, about 125 miles north of Damascus.

Psaki declined to detail any evidence that might substantiate the allegations or to say whether any toxin that might have been used would be considered a chemical weapon. Chlorine gas can be lethal and was used as a crude chemical weapon during World War I.

Both the Assad government and rebels reported a poison gas attack in Kafr Zeita on April 11; each side blamed the other. The United Nations has not determined what happened.

Asked about the allegation this month, Samantha Power, the U.S. ambassador to the United Nations, told ABC’s “This Week” that the reports of toxin use remained unsubstantiated. On Sunday, however, French President François Hollande gave some credence to the rebel allegations, telling Europe 1 radio that “several elements” suggest recent use of chemical weapons.

According to the Violations Documentation Centre, these videos come from media activist Abu Mahdi al-Hamwi, who was in Kaft Zeita in Syria on April 11.

The first video reportedly shows an explosive barrel dropping on the city.

Two more reportedly show victims in the hospital there.

“We’re examining allegations that the government was responsible. We take all allegations of the use of chemicals in combat . . . very seriously,” Psaki said. She said the United States is consulting and sharing information with other nations and organizations, including the Organization for the Prohibition of Chemical Weapons.

The OPCW is overseeing the destruction of Syria’s known stockpiles of lethal agents under an agreement reached last year. The organization has set an April 27 deadline for Syria to hand over all its chemical weapons for destruction. The head of the international chemical weapons mission for Syria estimated Saturday that the Assad government had removed or destroyed 80 percent of the material.

Activists say more than 150,000 people have been killed in Syria’s conflict, which is in its fourth year. Most were killed by conventional weapons, but opposition groups have long alleged that the Assad government has carried out small-scale chemical attacks against civilians in rebel-held areas.

Last summer, a chemical weapons attack near the capital, Damascus, killed hundreds of people. The Obama administration and allies blamed Assad, and President Obama said the deliberate gassing of civilians crossed a “red line” that required a U.S. response.

Planned airstrikes against Syrian military sites were called off in late August, however, because of the prospect that Assad might voluntarily give up his stockpiles. He quickly agreed to do so under a deal brokered by Russia and the United States.