UNITED NATIONS, April 18 (Xinhua) -- Airstrikes, artillery barrages, rocket fire and other heavy weapons are now part of the assault on the Libyan capital city of Tripoli and its outskirts, a UN spokesman said Thursday.

In total, 79 civilian casualties, including 18 deaths, have now been verified since the start of this recent round of violence, said Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres.

"The number of civilian casualties, and attacks on civilian property and infrastructure are worryingly on the rise," Dujarric told a regular briefing, adding that the toll was only of cases that could be verified. "We think there could be more casualties."

"The secretary-general is closely following developments in Libya, where airstrikes and sporadic clashes continue in southern Tripoli," the spokesman said.

The UN team in Tripoli is actively helping in the evacuation of civilians from conflict-affected areas wherever possible, he said. It is encouraging with "even limited humanitarian truces to allow for evacuations of civilians and wounded as an immediate priority."

The United Nations is also deeply concerned about reports of clashes between the two parties at the Tamanhint airbase near Sabha in the south and the potential for widening confrontations in other areas of the country, the spokesman said.

"We're frustrated at the continued fighting that we are seeing on the ground in Libya," Dujarric said. "The Libyan people once again are on the front lines of suffering, being hit by indiscriminate shelling, by use of heavy weapons in Tripoli."

Moving civilians out of conflict-affected areas remains a challenge, with nearly all main roads reportedly blocked and there being a high risk of being hit in crossfire, he said, adding that nearly all local trade has stopped in the areas affected.

The latest violence began April 4 when Gen. Khalifa Haftar's Libya National Army advanced on Tripoli, the seat of the internationally recognized government, striking the outskirts of the capital city.

Dujarric said 2 million U.S. dollars from the United Nations' Central Emergency Response Fund has been released to help civilians caught up in the fighting.

The money will help hospitals get the surgical and trauma kits they need, and provide food and other items to people uprooted by the fighting, he said. "They will also help safely relocate vulnerable migrants and refugees from detention centers in areas where airstrikes have been reported."

Under-Secretary-General Mark Lowcock, chief UN humanitarian aid coordinator, has urged all parties "to meet their obligations under international humanitarian law to protect civilians, civilian infrastructure and allow unimpeded access for humanitarian workers."

There is an urgent need to evacuate more of the most vulnerable people, Lowcock said.

Among the most vulnerable people are migrants from other countries in Africa stopped in Libya from their quest for a life in Europe. They have been held in detention centers on the heavily hit southern outskirts of the capital city.

The UN Refugee Agency and its partners have been relocating the migrants -- including women and children -- to sites closer to the more secure center of Tripoli.

"But we are not able to get to everyone we need to get to," said the spokesman.