A senior Egyptian al Qaida figure fighting in Syria has been killed in a US drone strike, an opposition monitoring group and relatives said.

The Britain-based Syrian Observatory for Human Rights said Rifai Ahmad Taha was killed in a strike on Tuesday in the north-western Idlib province.

Before joining al Qaida, Taha was a top figure in Egypt's notorious militant group Gamaa Islamiya, which massacred 58 foreign tourists in the ancient Egyptian city of Luxor in 1997. He was also allied with Osama bin Laden in Afghanistan.

The Observatory's chief Rami Abdurrahman said several al Qaida members, including Taha, were killed in the strike. He said one of the dead was identified as Abu Omar al-Masri - which is Arabic for Abu Omar the Egyptian - but that it was not clear if Taha was using that name. Taha was believed to be in his 60s.

In Egypt, a relative said Taha's wife and brother had received confirmation of his death.

In Washington, Department of Defence spokesman Matthew Allen said the US struck a vehicle killing several al Qaida militants. He added that officials are still assessing the strike.

"I can confirm that the US struck a vehicle killing several AQ militants," said Mr Allen. "The results of this strike are still being assessed."

On Wednesday, Syria's al Qaida branch known as the Nusra Front confirmed the death of Abu Firas al-Souri, a senior figure in the group, in another US air strike in Idlib.

Taha's relative said dozens of members of Islamic groups were paying condolences to the family at the home of his brother, Gharib, in the southern Egyptian village of Nagaa Dunqal. According to the relative, Taha told his family he believed he was being followed and three days before his death he called his brother from Syria to tell him that the Americans were monitoring his movements.

Taha was jailed in 2001 in Egypt under the rule of then-president Hosni Mubarak after being detained in Syria and handed over to Cairo. He was released after the long-serving leader was removed from power in 2011.

Before that he spent nearly three decades outside Egypt, including stints in Afghanistan and Sudan where bin Laden lived, and was also in Pakistan.

Taha was also involved in plotting the assassination attempt against Mr Mubarak during a visit to Ethiopia in 1995. The former Egyptian president was not harmed when his convoy was hit with bullets.

In the early 1980s Taha spent five years in jail after the 1981 assassination of Egyptian president Anwar Sadat by Muslim extremists.