Death toll rises after US airstrike in Syrian village, observer groups say At least 49 were killed, the Syrian Observatory for Human Rights said.

 -- U.S. warplanes struck a mosque compound in northwestern Syria Thursday, killing dozens of people, observer groups and eyewitnesses said today.

U.S. military officials confirmed the airstrike but said the target was a large gathering of al-Qaeda militants meeting in a building that they said was across the street from the mosque.

At least 49 people were killed and more than 100 injured in the attack in the rebel-held village of al-Jina in Aleppo’s countryside, according to the U.K.-based Syrian Observatory for Human Rights.

The targeted building was a center for Islam lectures that belongs to the mosque and is part of the same compound, the Syrian Observatory for Human Rights and eyewitnesses said. “If fighters were among those killed, they were attending a religious lecture, not fighting or preparing to fight,” Rami Abdulrahman, director of the Syrian Observatory for Human Rights, told ABC News.

The airstrike happened at 7 p.m. local time and was carried out by manned and unmanned aircraft targeting an al-Qaeda meeting, Pentagon spokesman Capt. Jeff Davis said at a press briefing today. He denied that the targeted building was a mosque, but said he had no information on whether the building was affiliated with a mosque.

Ahmad Qawwaf, a resident of al-Jina and an English teacher, said he was having dinner at a friend’s house when he heard the sound of planes and then a loud explosion Thursday evening, about five minutes before the call to nighttime prayer was set to begin. When he left, he said, he saw that the building for religious lectures affiliated with the mosque was hit.

“I saw ambulances and people covered in dust. And there were four bodies lying in the street,” Qawwaf told ABC News via a messaging app in Arabic. “The bodies were maimed … burns on the faces and the limbs.”

He said he visited the site again today and that rescue workers were still on the scene, trying to pull more people from the rubble. The White Helmets in Aleppo, a volunteer civil defense organization, has released videos of rescues after the airstrike.

"It was the mosque that was hit," media activist Darwish el-Saleh told ABC News.

He is from a neighboring village and visited the mosque in al-Jina after the attack. "The damage was overwhelming. There was a hole in the ground and bodies were filling the streets," he said, adding that he counted about 30 bodies Thursday.

Eric Pahon, a Pentagon spokesman, described the building as a “partially constructed community meeting hall” that intelligence indicated was a gathering place for al-Qaeda to “educate and indoctrinate al-Qaeda fighters.”

“Initial assessments based upon post-strike analysis do not indicate civilian casualties,” Pahon said. "We take all allegations of civilian casualties seriously and will investigate any credible allegations we receive.”

Even if the mosque wasn't the target, it could still have suffered damage because the buildings are so close to each other, said Chris Woods, director of Airwars, a nonprofit that tracks international airstrikes in Iraq and Syria.

“We are certainly not saying that the coalition deliberately targeted the mosque,” Woods told ABC News. “But based on all the evidence we’re seeing from the ground, videos, photographs and White Helmets testimony, the mosque was very heavily damaged last night and a significant number of people died.”

The U.S. military has launched a campaign against al-Qaeda in Syria, but U.S. airstrikes in Syria mostly target ISIS.

Thursday’s attack comes as the number of civilian casualties from U.S.-led coalition airstrikes against ISIS is growing, according to Airwars.

Since President Trump’s inauguration Jan. 20 through March 15, Airwars tracked 173 separate alleged incidents attributed to the coalition in which more than 1,000 civilians allegedly have died in Iraq and Syria.

“We’re seeing a fresh rise in civilian casualties,” Woods said. “Alleged and likely civilian deaths were already going up under the last time of Obama, but since Trump has come in we’ve seen a new jump.”

For the second month in a row, U.S. airstrikes have reportedly killed more civilians than Russian strikes, Airwars’ data for the month of February shows.

The battle against ISIS is at a fierce stage, but that alone does not explain the rise in alleged civilian casualties, Woods said.

“President Trump has very specifically instructed the Pentagon to come up with a plan to defeat ISIS that really restricts protection for civilians,” he said.

ABC News' Luis Martinez contributed to this report.