TUNIS (Reuters) - About 800 migrants in a government-run center in western Libya are being detained in worsening conditions without sufficient food or water, Doctors without Borders (MSF) said.

Migrants gather at a safe house in the town of Bani Walid, Libya March 25, 2018. Picture taken March 25, 2018. REUTERS/Ismail Zitouny - RC1B0179C680

Many of the migrants have been trapped for more than five months in the center of Zuwara, about 100 km (62 miles) west of Tripoli, where some arrived malnourished after being held by smuggling networks, MSF said in a statement late on Thursday.

“The situation is critical,” said MSF emergency program manager Karline Kleijer.

The center is one of several nominally run by the internationally recognized government in Tripoli. They house migrants who are rounded up on the streets or intercepted by Libya’s EU-backed coastguard as they try to leave for Italy by boat.

The centers only hold a fraction of the hundreds of thousands of migrants in Libya. Most live in communities or are held by smuggling networks.

Many detention centers have been closed in recent months as migrants are repatriated under a voluntary returns program run by the International Organization for Migration (IOM) or through bilateral flights.

Activists say conditions for migrants in Libya that were already dire may have deteriorated further since last summer, when numbers reaching Europe dropped sharply following an Italian-led push to cut off crossings. Some are being held for longer by smugglers who use torture to extort money from migrants’ families, they say. [nL8N1S44G1]

Zuwara itself used to be a major smuggling hub before a local backlash against smugglers in 2015. Recently, boat departures from the city have picked up again, aid workers say.

More than 500 people had been detained in the city in the past 15 days, according to MSF.

The U.N. refugee agency airlifted 88 migrants from Zuwara to another detention center in Tripoli on May 1 in order to identify the most vulnerable cases for evacuation.

Libyan authorities have also transferred some migrants in an effort to reduce severe overcrowding at the Zuwara center and the IOM has begun a process to repatriate others.

“However, there is no solution in sight for many of the estimated 800 people who remain in the detention center in Zuwara,” MSF said.

“We strongly urge all international agencies with a presence in Libya, representatives from the countries of origin, and the Libyan authorities to do everything they can to find a solution for these people over the next few days,” said Kleijer.