Washington (AFP) - The American government is investigating whether Al-Qaeda's number two has been killed in Syria, an official told AFP Tuesday, amid reports of a US strike in or around Idlib.

The official, who spoke on condition of anonymity, said that agencies were working to confirm whether Abu Khayr al-Masri is dead, in what would be a major counterterrorism coup for Donald Trump early in his presidency.

Al-Masri is a son-in-law of Qaeda founder Osama bin Laden and is believed to be deputy to the group's current leader Ayman al-Zawahiri.

"Certainly if the reports are true it would be welcome news," said Pentagon spokesman Navy Captain Jeff Davis.

Trump has put tackling so-called "radical Islamic extremism" at the top of his political agenda.

He is currently considering a review of the fight against the Islamic State group, aiming to intensify the campaign and is poised to revive efforts to ban travels from certain Muslim-majority countries.

The revised travel ban could come as early as Wednesday, White House officials said.

Egypt-born al-Masri, 59, is one of the most prominent figures in Al-Qaeda to have roots in the era before the September 11, 2001 attacks, according to the Soufan Group, a private security and intelligence consultancy.

"It was in al-Masri's guesthouse in Kabul, Afghanistan, that Khalid Sheikh Mohammed briefed top Al-Qaeda leaders about the planning of the September 11, 2001 attacks," the Soufan Group said.

His presence in Syria's northwestern Idlib underscores the importance that country has gained in Al-Qaeda's strategy, analysts said.

Al-Masri, also known as Abdullah Muhammad Rajab Abdulrahman, joined Zawahiri in the Egyptian Islamic Jihad group in the 1980s before they enlisted with Bin Laden in the 1990s.

US intelligence believe al-Masri was involved in the 1998 bombings of US embassies in Kenya and Tanzania.

He was detained with several other Al-Qaeda figures in 2003 in Iran and held until 2015, when they were traded for the release of an Iranian diplomat who had been seized by Al-Qaeda's Yemen branch.

Story continues

Charles Lister of the Middle East Institute said that if al-Masri's death is confirmed, would be the "biggest blow to Al-Qaeda since the killing of Nasir al-Wuhayshi in Yemen in June 2015."

Wuhayshi was the leader of Al-Qaeda in the Arabian Peninsula.

Lister described al-Masri as "jihadi royalty," as a longstanding member of Al-Qaeda's central Shura Council and "one of Ayman al-Zawahiri's closest long-time confidants."

His death would "almost certainly necessitate some form of response, whether from Syria or elsewhere in the world," he said.

According to Treasury Department sanctions al-Masri was previously responsible for coordinating Al-Qaeda's work "with other terrorist organizations."

He was born in the Nile Delta city of Kafr al-Shaykh in November 1957, in the midst of Gamal Abdel Nasser's rule.