(Adds UN report on displaced people)
By Ayman al-Warfalli and Ahmed Elumami
BENGHAZI, Libya, Sept 4 (Reuters) - Government forces and helicopters belonging to a Libyan renegade general bombed ammunition sites of suspected Islamist militants in the eastern city of Benghazi, a military commander and residents said.
In another sign of Libya's descent into anarchy, the U.N. mission said fighting in the two main cities Tripoli and Benghazi has displaced 100,000 people. Some 150,000 people, including foreign workers, have fled the oil producing country.
Islamist forces have been trying to take the civilian and military airport from government forces in Benghazi, part of the widespread unrest in the North African country three years after the ouster of Muammar Gaddafi.
Western powers and Libya's neighbours fear the country will turn into a failed state. A weak government is unable to control former rebels who helped topple Gaddafi but now fight each other for power.
Wanis Bukhamada, commander of army special forces in the port city of Benghazi, told Reuters his forces had attacked with artillery several ammunition stores in camps held by Islamists late on Wednesday.
Residents also heard helicopters and huge blasts lighting up the night sky in a Benghazi suburb. On Thursday war planes could be also heard.
Benghazi, where the headquarters of state oil firms are located, has been a war zone since renegade army general Khalifa Haftar declared war in May on Islamists roaming the area unchallenged.
He has allied himself with the special forces but despite that alliance, Islamists have managed to overrun several army camps in Benghazi.
Libya's government and elected House of Representatives has relocated to the remote eastern city of Tobruk after a separate armed group seize the capital Tripoli and most government institutions last month.
The new Tripoli rulers have set up a rival parliament and government not recognized by the international community.
"Serious violations of international human rights and humanitarian law are taking place in the Libyan cities of Tripoli and Benghazi with dire consequences for civilians and civilian infrastructure," the U.N. Mission in Libya said in a report.
"Fighters appear to disregard the likely impact of their action on civilians and have inadequate training and discipline. In addition, the use of badly maintained and faulty weapons and ammunition increases inaccuracy," the report said.
Like most foreign embassies, the mission in Libya has left the country to escape the fighting. (Additional reporting by Feras Bosalum; Writing by Ulf Laessing; editing by Dominic Evans)