Militias in western Libya vowed Friday to confront a rival army commander's attempt to seize the capital, Tripoli, raising fears of renewed violence in the oil-rich nation after a series of U.N. led peace efforts.

The military push by Gen. Khalifa Haftar's Libyan National Army (LNA), which is allied to a parallel administration based in the east, marked a dangerous escalation of a power struggle that has dragged on since the overthrow of Moammar Gadhafi in 2011. Haftar, who has been leading the LNA, based in Benghazi, is not recognized by the international community, as the elected parliament of the country is centered in Tripoli. However, Haftar, with financial and political support from certain countries, including Gulf states, has appeared as a primary actor in the war-torn country. The dispute between Benghazi and Tripoli resulted in a U.N. mediated cease-fire last year. However, the cease-fire has been violated after Haftar's recent westward move.

LNA forces on Thursday took Gharyan, about 80 kilometers south of Tripoli, after skirmishes with forces allied to Tripoli-based Prime Minister Fayez Serraj. But they failed to take a checkpoint about 30 kilometers west of the capital in a bid to close the coastal road to Tunisia. An LNA-allied militia withdrew overnight from so-called Gate 27, leaving it abandoned in the morning, a Reuters reporter said. Meanwhile militias allied to the U.N.-backed Tripoli government moved more machine gun-mounted pickups from the coastal city of Misrata to Tripoli to defend it against Haftar's forces.

The advance by Haftar's forces, which came as the United Nations prepares to convene a conference later this month on organizing delayed elections, prompted U.N. Secretary-General Antonio Guterres to voice his "deep concern." Guterres was in Tripoli for talks with Sarraj, when the offensive was announced.

Turkey urged restraint while calling on rival sides "to avoid attempts that would harm the spirit of national accord in Libya." "We closely follow the recent military escalation in the west of Libya. We believe that the present division in Libya can only be overcome through intra-Libyan dialogue," Turkish Foreign Ministry said in a statement. The statement also underscored the importance of holding the U.N.-facilitated National Conference, which is planned to take place in Ghademes on April 14-16, aimed at bridging the gap among Libya's factions and draw a road map for new elections and end the country's split.

Amid a military offensive against the U.N.-backed government in Libya, chaos and a new migration crisis must be avoided, the European Parliament's president said Friday. "The European Union must take immediate action," Antonio Tajani said in a written statement. "Military action is not the solution to the Libyan crisis," he said. "A new conflict would only cause further loss of life and enormous damage to the country and its people."

Libya has remained dogged by turmoil since 2011, when a NATO-backed uprising led to the ouster and death of former President Gadhafi after more than four decades in power. Since then, Libya's stark political divisions have yielded two rival seats of power, one in Tobruk and another in Tripoli, and a host of heavily armed militia groups.