Civilians reported dead after US conducts counterterrorism raid in Syria.

 Washington (CNN)US Special Forces conducted a "successful" counterterrorism mission in northwest Syria Wednesday evening, the Pentagon said, but offered few other details.

But witnesses and rescue workers told CNN that shelling and explosions preceded an airdrop of US forces shortly after midnight and targeted a house in the Syrian-Turkish border area of Atmeh, in the rebel enclave of Idlib.

One witness in Atmeh, who asked not to be named for security reasons, said that machine gunfire erupted from at least three helicopters flying overhead, followed by an explosion some minutes later.

The witness also said he heard what sounded like drone strikes, and said HTS forces were preventing civilians from entering the area.

The witness said two of the three helicopters he saw landed an hour after the clashes began.

"I saw from a distance that there were machine guns shooting back from the ground towards the helicopters."

"Around 3:20 a.m., the helicopters left and I saw a faraway light which looked like a fire," said the witness.

"I heard from a distance a person who is speaking Arabic in an Iraqi accent asking for families to evacuate the area and they will be safe," said the witness.

"More information will be provided as it becomes available," the statement said.

The three-sentence Pentagon statement did not disclose a target for the special operations mission or whether there was any indication of civilian casualties.

Central Command opened an investigation into the possibility of civilian casualties from the strike, but the Pentagon was unable to provide updates at the time.

One month later, the military carried out a drone strike against Abdul Hamid al-Matar, a senior al Qaeda leader, Central Command said.

And then in December, the military targeted Musab Kinan, a senior leader of al Qaeda affiliate Hurras al-Din, near Idlib.

In September, the military targeted a senior al Qaeda leader near Idlib, Syria, according to a statement from Central Command.

The US has repeatedly targeted al Qaeda and its affiliates in northwest Syria, with the Pentagon acknowledging at least one strike in recent months may have resulted in civilian casualties.

The area has a heavy presence of Hay'at Tahrir al-Sham (HTS) forces, that were formerly affiliated to al Qaeda.

CNN has reached out to Central Command.

Pentagon press secretary John Kirby said in a statement late Wednesday night that the mission was conducted by US Central Command, which controls military operations and activities in the Middle East.

There were no US casualties, according to the Pentagon.

Sources on the ground reported multiple fatalities.