CAIRO -- Recent clashes between rival Libyan militias for control of the capital Tripoli have displaced more than 18,000 people, the U.N. said, and prompted the prosecutor of the International Criminal Court to warn Tuesday that she could investigate and possibly prosecute new offences.

The self-styled Libyan National Army, aligned with a rival government in the east, launched a major military offensive on April 5 to take Tripoli, igniting clashes with rival militias allied with the U.N.-backed government.

ICC Prosecutor Fatou Bensouda, who was already investigating crimes in Libya, said in a statement that she is “deeply concerned” about the escalation of violence and called on military commanders to prevent war crimes.

She said she “will not hesitate to expand my investigations and potential prosecutions to cover any new instances of crimes falling within the Court's jurisdiction.”

U.N. spokesman Stephane Dujarric said in New York on Monday that the International Organization for Migration reported that 13 civilians were among the 146 killed so far in the clashes that have wounded 614 people including 35 civilians.

He said the number of civilian causalities “reflect only those cases that could be individually verified and should be considered a minimum.”

Dujarric also said around 3,000 migrants remain trapped in detention centres in, and close to, conflict areas. And “in some cases guards have abandoned the detention centres leaving detainees to their own devices without basic life-sustaining supplies such as food or water,” he said.

On the ground, Hifter's media office said clashes have been ongoing for days in the town of Ain Zara about 15 Kilometers (9 miles) east of Tripoli.

It said clashes were taking place on the road that links the city to the Tripoli international airport. The LNA said earlier this month that they captured the airport but rival militias said they reclaimed the facility. The Tripoli airport has not been functional since fighting in 2014 destroyed much of the facility.

The battle for Tripoli could ignite civil war on the scale of the 2011 uprising that toppled and killed longtime dictator Moammar Gadhafi. That conflict led to Bensouda's ongoing probe after the U.N. Security Council called for an investigation.

Since Gahdafi's ouster, Libya has been governed by rival authorities in the east and in Tripoli, in the west, each backed by various militias and armed groups fighting over resources and territory.