The UN has called for an "urgent" resumption of Mediterranean rescues after 43 migrants died in a shipwreck off the coast of Libya while attempting to reach Europe. 

The first tragic event of its kind in the Central Mediterranean since the start of the year, the International Organisation for Migration (IOM) and the UN High Commission for Refugees (UNHCR) wrote they were "deeply saddened" by the tragedy.

The shipwreck took place on Tuesday, according to the UN agencies, after a boat coming from the Libyan city of Zawya capsized several hours after its departure. Apparently, its engine stopped working under poor sea conditions.

Survivors, the majority of whom came from the Republic of Côte d'Ivoire, Nigeria, Ghana and Gambia, said those who died were men from West African countries.

The crossing over the central Mediterranean to Europe is considered the most deadly migration route in the world. 

In their statement, the IOM and the UNHCR feared that "due to the limited ability to monitor routes", the real number of deaths last year in the area "could be much higher".

"This loss of life highlights once more the need for re-activation of state-led search and rescue operations, a gap NGO and commercial vessels are trying to fill despite their limited resources," they added.

The agencies also called again on the international community to quickly shift its approach to the crossings in the Mediterranean.

"This includes ending returns to unsafe ports, establishing a safe and predictable disembarkation mechanism followed by a tangible show of solidarity from European states with countries receiving high numbers of arrivals," the statement said.

Libya is now a major route for irregular migration to Europe after years of political instability caused by the NATO-backed overthrow of Moamer Kadhafi in 2011.

While many have drowned in the Mediterranean, thousands more have been intercepted by the Libyan coastguard, backed by the EU, and returned to Libya, where they mostly end up in detention, and often in horrific conditions.

"The situation for migrants and refugees in Libya remains extremely precarious," the UN said. 

"Arbitrary arrests and arbitrary detention in the direst of conditions continue. Many are victimised and exploited by traffickers and smugglers, held for ransom, tortured, and abused."

Despite acknowledging the Libyan authorities' efforts to combat trafficking and smuggling, they called for further action.

"Should inaction and impunity prevail, more avoidable and tragic loss of life can be expected," they said.