Afghan Taliban leader Mullah Akhtar Mansour and another combatant are believed to have been killed in a US drone strike in Pakistan, according to a US official.

US President Barack Obama reportedly authorised the strike.

The strike took place at about 6am local time (11am Irish time), the official said, which would have placed it late on Friday night in the target area.

Multiple US drones targeted the men as they rode in a vehicle in a remote area in Pakistan along the Pakistan-Afghanistan border, southwest of the town of Ahmad Wal,the official said.

Meanwhile, a new message purporting to come from the spokesman of the self-proclaimed Islamic State group has called on followers to launch attacks on the US and Europe during the Islamic holy month of Ramadan, which begins in early June.

The authenticity of the audio clip, purporting to be from Abu Muhammad al-Adnani and distributed by Twitter accounts that usually publish IS statements, could not be verified.

The militant group, which seeks to establish a caliphate across the Middle East and beyond, has claimed deadly attacks over the past year on civilians in France, Belgium and the US.

However, the message made no mention of the EgyptAir flight that crashed into the Mediterranean in unexplained circumstances, amid speculation by Egyptian, French and American officials that a jihadist attack was the most likely cause.