UNITED NATIONS, April 9 (Xinhua) -- As troops opposing the internationally recognized government battle in the outskirts of Tripoli, Libya, the United Nations has appealed for an end to violence and for the protection of civilians.

The UN Office for the Coordination of Humanitarian Affairs (OCHA) said some 4,500 individuals have been displaced from the affected Tripoli neighborhoods to comparatively safe areas in the capital. However, concerns remain for civilians caught in conflict-affected areas, who are unable to leave their homes amid the ongoing fighting, said Stephane Dujarric, spokesman for UN Secretary-General Antonio Guterres.

Guterres himself on Monday called for a halt of all military operations in and around Tripoli to de-escalate tension and prevent "an all-out conflict."

A UN-planned conference in Libya to bring all sides together was set to begin Sunday but has to be postponed because of the advancing Libyan National Army under Khalifa Haftar to the capital.

The UN Secretary-General's Special Representative in Libya Ghassan Salame said in a statement issued in Tripoli earlier Tuesday that he is determined to hold the Libyan National Conference at the earliest possible date, as it remains a historic opportunity.

"We also cannot ask Libyans to attend a conference to the backdrop of artillery shelling and air raids as we must ensure that all of those who expressed willingness to respond to this historic and national event from all over the country are able to attend and are able to voice their opinions freely," he said.

Salame vowed to work "to the fullest possible extent" to enable the Libyan National Conference to take place as soon as possible.

The UN High Commissioner for Refugees Filippo Grandi, who was at UN Headquarters on Tuesday to brief the Security Council on the worldwide refugee situation, told reporters just how dangerous the situation around Tripoli was.

"This (Tuesday) morning, my colleagues, braving the bullets, literally, have evacuated 150 refugees from a detention center in Ain Zara, which is near Tripoli, to one transit center, the only one, that we have been able to establish after months of negotiations with the Libyan authorities," he said. "But, they took a risk to their lives to save these 150 people."

"If the situation becomes worse I fear that even these small gestures that we can do to help at least some people will become impossible," he said.

The detention center is one of several that have been set up by the Tripoli government to house refugees and migrants from other parts of Africa seeking to cross the Mediterranean to asylum in Europe.

At least 35 fatalities, including civilians, have been recorded since Khalifa's push began last week, according to published reports.

The World Health Organization reported that among the dead are two doctors who had been providing critically needed services to civilians in Tripoli. The agency reiterated that targeting health care workers and health facilities is against international humanitarian law.

The UN High Commissioner for Human Rights Michelle Bachelet on Tuesday joined the secretary-general in reminding all parties in the conflict in Libya of their obligations under international law to ensure the protection of civilians and civilian infrastructure. She urged all parties to take measures to ensure civilians do not bear the brunt of the fighting and highlighted the need to ensure the protection of extremely vulnerable people, including refugees and migrants.

An appeal of 202 million U.S. dollars for the humanitarian response for Libya this year is just 6 percent funded, said Dujarric.