Emergency aid workers in the area said on Tuesday that helicopters dropped barrels that may have been full of chlorine gas over the town of Saraqeb, in western Syria, the same area where a Russian helicopter was downed the previous day.

Members of different rescue groups confirmed that 33 people were admitted to the hospital following the apparent attack, which occurred late Monday night. It was not clear if the helicopter belonged to the Syrian regime or to Russia.

Ten of the patients were children, a member of the White Helmets told dpa news agency. Another emergency aid group, Syria Civil Defense, posted a video on YouTube showing people being handed oxygen masks.

If exposed to chlorine gas, people can have problems breathing and foam blood from their mouths. President Bashar al-Assad has been repeatedly accused of using the toxic substance during the country's five-year conflict.

Russian helicopter shot down

The alleged attack came shortly after a Russian helicopter was shot down near the same city earlier on Monday. Russian state news agency Interfax said the aircraft was carrying three crew members and two officers and had just delivered aid to the war-torn city of Aleppo.

"As far as we know from the information we've had from the Defense Ministry, those in the helicopter died. They died heroically, because they were trying to move the aircraft away to minimize victims on the ground," said Kremlin spokesman Dmitry Peskov.

If confirmed, the attack will be the deadliest against Russia since it entered the conflict in Syria last year.

No group has claimed responsibility for the downing of the helicopter.

blc/kms (Reuters, dpa)