Syrian rebels, including Sunni extremists, stormed a village and battled pro-regime militiamen, killing more than 60 Shiite fighters and civilians in an attack steeped in the sectarian hatreds that increasingly characterize the civil war, activists said Wednesday.

In the raid, which comes at a time when the West is worried that extremists are increasingly joining the rebellion, the victorious fighters raised black Sunni Islamist flags over the eastern village of Hatla. In amateur videos, the fighters — some wearing al-Qaida-style headbands — vented anti-Shiite slurs and fired guns into the air.

“The homes of the infidel Shiites were burned,” the voice behind the camera in one video shouted as smoke rose in the background from several houses.

In another video, proud fighters pulled blankets off corpses to reveal them; one had a wound to the head. A gunman talking to the camera gloated, saying, “This is your end, dogs.” The videos appeared genuine and conformed with other reporting on the events.

The attack Tuesday on Hatla, in Syria’s Deir el-Zour region near Iraq, underlined the increasingly sectarian nature of the conflict.

The regime called it a “massacre,” and some opposition members expressed concern about the nature of the attack. The U.S. and other Western nations have been hesitant to arm the outgunned and outmanned rebels because of Sunni jihadi radicals among their ranks.

The uprising began more than two years ago with peaceful protests against President Bashar Assad but later grew into a civil war that has killed more than 80,000 people.

Most of the armed rebels in Syria are from the country’s Sunni majority, while Assad has retained core support among the minorities, including his own Alawite sect, an offshoot of Shiite Islam, along with Christians and Shiites.

In the past year, sectarian bitterness has grown in the conflict. Each sect has been accused of massacres against the other, and Sunni and Shiite fighters from other countries have increasingly joined the battle.

But the sense of the fight being a battle between faiths was taken up a notch after Shiite guerrillas from Lebanon’s Hezbollah helped Assad’s forces take the rebel stronghold of Qusair last week. Some fighters in Hatla can be heard in the video calling the attack “the first revenge for Qusair.”

An activist based in Deir el-Zour said the rebel attack was in retaliation for an attack Monday by Shiites from Hatla that killed four rebels.

The town is home to several thousand people, about 30 percent of them Shiites, and was considered a pro-regime community in the Euphrates River valley, where rebels — including the al-Qaida-linked group Jabhat el-Nusra — have taken over much of the territory.

Activists said many of the dead Wednesday were pro-government militiamen who had earlier attacked the rebel bases. But there were also many civilians killed in the raid, according to the Syrian Observatory for Human Rights, a British-based anti-Assad group that has a large network of activists.

More people were believed killed in the fighting, including many children and civilians, according to an opposition figure who was informed of details of the attack but spoke on condition of anonymity because he feared retaliation.

The Observatory said thousands of rebels took part in the attack, and at least 10 were killed. A Facebook page of Islamist activists in Deir el-Zour province said Jabhat el-Nusra and rebel fighters from the Free Syrian Army, the main rebel umbrella group, were involved. There was no immediate confirmation from the group, which includes many non-Syrian jihadists.