AMMAN: Two jihadists including a brother-in-law of slain Al-Qaeda in Iraq leader Abu Musab al-Zarqawi have been killed in clashes with Syrian regime forces, a senior Jordanian Salafist said on Thursday.

"Adam Abulmutasem and Mohammad Jarad, who are in their 20s, were killed two days ago in clashes with regime troops in the southern province of Sweida," Abed Shehadeh, known as Abu Mohammad Tahawi, told AFP.

"Jarad was the brother-in-law of Abu Musab al-Zarqawi," Tahawi said.

Jordanian-born Zarqawi was killed in an air strike by the US military in Iraq in 2006.

The two jihadists who were killed in Syria this week fought alongside the jihadist Al-Nusra Front, according to Tahawi.

Nusra, which first gained notoriety for its suicide bombings in Syria, has evolved into a formidable fighting force leading attacks on battlefronts throughout the embattled country.

Its extremist tactics and suspected affiliation to the Al-Qaeda offshoot in Iraq have landed it on the US list of terrorist organisations.

"Twenty-two out of the 350 Jordanian jihadists currently fighting in Syria have been killed," including the "mufti" of Nusra in Daraa, Tahawi said.

Jordan arrested more than a dozen jihadists in April and June as they tried to infiltrate Syria, where insurgents are fighting to oust the regime of President Bashar al-Assad.