The death toll of the pre-dawn aerial assault in eastern Syria has risen to 15, according to a war monitor group.

The Syrian Observatory for Human Rights said among those killed, 14 were members of the Iranian Islamic Revolution Guard Corps, including a high-ranking Iranian advisor responsible for a targeted communications center.

The attacks also injured 24 military personnel and 10 civilians, said the watchdog group.

The Syrian Defense Ministry, meanwhile, put the death toll at eight, including seven "military personnel" and one civilian, without divulging any information on Iranian-backed militia fighters.

While the defense ministry blamed the U.S. forces for the airstrikes, the Britain-based watchdog group said it could not confirm the party responsible for it, saying they were possibly conducted by the U.S. military with possible involvement of Israel.

However, Enab Baladi, a Syrian nonprofit media organization, reported that the United States did not carry out any attack in Syria in the past 24 hours, quoting an anonymous official from the U.S. Defense Department.