The US military killed senior Al Qaeda leader Abdul Hamid Al-Matar in a drone strike in Syria on Friday, a US Central Command spokesman said.
"The removal of this Al Qaeda senior leader will disrupt the terrorist organisation's ability to further plot and carry out global attacks threatening US citizens, our partners, and innocent civilians," US Army Maj John Rigsbee said in a written statement.
The strike comes two days after a US outpost in southern Syria was attacked with a co-ordinated drone attack, but there were no reports of any American casualties, officials said.
“Explosions resounded from Al Tanf base used by the US-led coalition” fighting ISIS, the Syrian Observatory for Human Rights said from Britain, without specifying who was responsible for the attack.
One official said one of the drone strikes hit the US side of the Al Tanf garrison, while one may have hit the side where Syrian opposition forces are based.
The garrison was set up when ISIS fighters took control of eastern Syria along the border with Iraq, but after the militants were driven out, it became part of the larger US strategy to contain Iran's military reach in the region.
Maj Rigsbee did not say whether the US drone strike was carried out in retaliation.
This is a developing story.
Agencies contributed to this reporting