Pro-Haftar Libyan planes took part in Egyptian air strikes

The air force loyal to Libya's strongman Khalifa Haftar said on Saturday it took part in Egyptian airstrikes on militant positions in the country after a deadly attack on Egypt's Copts.

Egypt launched six air strikes on militant camps in Libya's eastern city of Derna on Friday, hours after masked gunmen attacked a bus carrying Coptic Christians south of Cairo, killing at least 29 people.

The Islamic State group on Saturday claimed responsibility for the attack, the latest in a series of IS strikes that have killed more than 100 Copts in Egypt since December.

Haftar's forces carried out a "joint operation" with Egypt in Derna, the air force said in a statement carried by the LANA news agency loyal to Libya's eastern administration.

Egypt used French-built Rafale fighter jets to target military camps and the headquarters of the pro al-Qaeda Majlis Mujahedeen Derna, which controls the city, it said.

"The operation was a success and the losses of the al-Qaeda terrorists were heavy in casualties and equipment," the statement said.

The UN-backed Government of National Accord (GNA), opposed by Haftar, denounced the raids as a violation of its sovereignty.

"Whatever the pretext, we reject any action that undermines the sovereignty of our country. There is no justification for the violation of the territory of other countries," a GNA statement said.

Derna was known as a bastion of extremists even before the 2011 uprising that toppled and killed Libya's longtime dictator Muammar Gaddafi.

After the revolt, the al-Qaeda-linked Ansar al-Sharia slowly spread its presence to Derna.

In 2014, some militants defected to join IS, which took control of Derna.

Pro-al-Qaeda elements opposed to IS banded together to form Majlis Shura al-Mujahedeen Derna to fight both the group and Haftar's forces, in 2015 expelling the extremists from the city.

Haftar's forces regularly carry out air raids on positions of the jihadi alliance.

Libya's Islamists accuse Haftar allies Egypt and the UAE of taking part in these strikes.