United Nations aid agencies criticized European countries on Tuesday for not allowing migrants to disembark at safe ports, after more than 140 people rescued at sea were taken to a detention center in Misrata, Libya.

An estimated 170 migrants were lost in the Mediterranean in two incidents involving dinghies that left from Libya and Morocco, migrant organizations said on Saturday.

In all, 203 passengers have drowned at sea trying to reach Europe in January while 4,883 have arrived, mainly in Spain, Greece and Italy, the International Organisation for Migration (IOM) said.

Private rescue ships have been restricted from conducting search and rescue operations in the Mediterranean, putting more lives unnecessarily at risk, the UN High Commissioner for Refugees said.

"IOM confirmed yesterday [Monday] that the Sierra Leonean flagged cargo vessel Lady Sham returned 144 rescued migrants to Libya. It remains unclear when and from where these individuals departed," IOM spokesperson Joel Millman told a Geneva briefing.

"IOM staff counted 26 women and four children among those rescued and taken to a detention centre in Misrata," he said.

'Appalling treatment'

Libya, wracked by violence, is no refuge, the UNHCR said.

"In Libya's current context, where outbreaks of violence and widespread human rights violations prevail, no rescued refugees and migrants should be returned there," said UNHCR spokesperson Charlie Yaxley.

"It's been well-documented at this point that the people in these detention centres face pretty appalling treatment, many report going hungry for days on end, not being able to receive dire urgent medical care that they require. Others allege to have been tortured," he said.

Matteo Salvini, Italy's interior minister, who has closed off Italian ports to humanitarian rescue vessels since a populist government came to power in mid-2018, has said the ports would remain closed to deter human traffickers.

UNHCR denounced "politicking around sea rescues" by European states that have restricted aid groups from conducting missions.

"Currently, rescue at sea has been taken hostage by politics ... decisive leadership that taps into fundamental values of humanity and compassion is sorely needed," UNHCR's Yaxley said.