U.N. agencies said on Monday they were trying to provide urgent help to large numbers of migrants held and then stranded in the smuggling hub of Sabratha as rival factions battled for control of the city.

At least 4,000 migrants, including pregnant women, newborn babies and unaccompanied children, have been transferred from informal camps and housing to a hangar in the city since the clashes ended on Friday, the International Organization for Migration (IOM) said. The U.N. refugee agency, UNHCR, said some 6,000 had been held at the informal sites.

“They come walking in groups ... for example there were various groups that came on Sunday -- 50, then 100 and 200 at night,” said Jayash. There were about 1,700 migrants currently in Zuwara “in desperate need of help”, he said.

Sabratha has been the most common point of departure for mostly sub-Saharan African migrants trying to cross the Mediterranean by boat from Libya.

But the number of crossings dropped sharply in July after an armed group struck a deal with officials from the U.N.-backed government in Tripoli to block departures, under pressure from Italy and other European Union member states.

That set off three weeks of fighting among rival factions that left at least 43 dead and 340 wounded, according to a new health ministry toll, and ended with the withdrawal of the armed group. The migrants who have since been rounded up were being held at sites that the group had controlled, local officials said.

“We are seriously concerned by the large number of migrants caught up in recent developments in Sabratha,” Othman Belbeisi, IOM Libya chief of mission, said in a statement.

Some migrants are being sent on to detention centers elsewhere in western Libya that are nominally under the control of the Tripoli government.

IOM officials say those centers, which were housing some 5,000 migrants, risk being overwhelmed by the new arrivals. Conditions in the centers are often dire and abuse widespread.

“Alternatives to detention must be found for migrants in Libya. In the meantime, IOM continues to provide direct humanitarian, health and psychosocial assistance to meet the urgent needs of the thousands of migrants being affected,” Belbeisi said.

The head of Sabratha’s department for countering illegal migration told Reuters on Saturday that help was badly needed as some migrants had received no food or water for six days.

The UNHCR said it had approached Libyan authorities to ensure that refugees among the migrants were freed from detention.