A jihadist who once fought in the Khorasan group offered messages of condolences on Twitter over the death of the Al-Qaeda offshoot group's alleged leader, the SITE monitoring group said Saturday.

The messages appeared to provide confirmation that US airstrikes in Syria might have killed Khorasan leader Muhsin al-Fadhli, a long-standing Qaeda operative.

SITE said a series of tweets from the jihadist, identified as a member of Al-Qaeda, expressed condolences for the deaths of Fadhli and another Khorasan leader, Abu Yusuf al-Turki.

The US based monitoring group said the jihadist in Twitter postings dated September 27, 2014, also lamented the situation on the ground in Syria with US-led coalition forces striking Islamic State (IS) forces, SITE said.

The strikes by US warplanes and cruise missiles targeted the Islamic State movement as well as the until recently little-known Khorasan group, which Washington has said is plotting attacks against US targets.

Washington last week expanded its air strikes, which for weeks had focused on IS targets in Iraq, to include Syria as well.

The United States and its coalition partners aim to destroy the Islamic State group, which controls a swath of territory in Iraq and Syria, has murdered two US journalists and a British aid worker and is locked in a brutal war with Iraqi and Kurdish authorities.