A member of the Libyan National Army, commanded by renegade general Khalifa Hifter, heads out of Benghazi to reinforce the troops advancing to Tripol on Sunday. (Esam Omran Al-Fetori/Reuters)

Clashes between a renegade eastern commander’s forces and pro-government militias escalated Monday, increasing the death toll and forcing thousands of residents of the Libyan capital to flee their homes while trapping thousands more.

Gen. Khalifa Hifter’s forces have continued to push toward Tripoli, even as the United States, the United Nations and Arab nations have urged him to halt his offensive. On Monday, the European Union joined the chorus of voices as its head of foreign policy, Federica Mogherini, called for a “full implementation of the humanitarian truce” and “a return to the political track.”

But that scenario appears increasingly distant. The United Nations’ top humanitarian official in Libya said that more than 2,800 people had fled the violence in and around Tripoli, while wounded and vulnerable civilians are so isolated that emergency responders cannot reach them.

Hundreds, if not thousands, of migrants and refugees also are trapped in detention centers in active conflict zones, their misery compounding every day, according to the U.N. officials.

“The United Nations continues to call for a temporary humanitarian truce to allow for the provision of emergency services and the voluntary passage of civilians, including those wounded, from areas of conflict,” Maria do Valle Ribeiro, the U.N. humanitarian coordinator for Libya, said in a statement.

The clashes south of the capital have killed at least 25 people, including fighters and civilians, and wounded 80, a spokesman for the Tripoli-based Health Ministry told Reuters on Monday.

Also Monday, an airstrike on Tripoli’s Mitiga airport forced its shutdown and stranded passengers. It was the capital’s only functioning airport.

Hours later, the U.N. special envoy in Libya, Ghassan Salamé, condemned Hifter’s forces for the airstrike, declaring that “this attack constitutes a serious violation of international humanitarian law, which prohibits attacks against civilian infrastructure.”

The 75-year-old Hifter, a U.S. citizen who lived in exile in Northern Virginia for years, is aligned with a rival government based in the eastern city of Tobruk. He returned to Libya during the 2011 revolution and subsequent NATO intervention that toppled dictator Moammar Gaddafi and led to his killing.

Hifter has long coveted Tripoli, where Libya’s oil revenue flows to and where the central bank — which pays the salaries of soldiers and civil servants — is based. In the past few months, Hifter’s forces — a constellation of militias calling themselves the Libyan National Army — have swept through the south and quickly pushed north toward Tripoli.

The tensions in Tripoli are the worst since conflict erupted between Hifter and rival militias in 2014, and they threaten to plunge the country into a full-blown civil war.

A counteroffensive by the U.N.-installed and Western-backed Tripoli government has slowed Hifter’s advance. The Tripoli government, with no army of its own, has relied on dozens of militias to remain in control, including many from other cities, particularly Misurata and Zintan.