The UN refugee agency has defended private aid groups rescuing migrants in the Mediterranean. Some of them have been accused in Italy of cooperating with smugglers in Libya. UN High Commissioner for Refugees Filippo Grandi said on Sunday there needed to be a greater effort to rescue a rising number of migrants using Libya as a springboard to reach Europe by boat. "This is a matter of life or death which appeals to our most basic sense of humanity and should not be called into question," Grandi said.  "The tireless efforts of the Italian Coast Guard, in coordination with Frontex, the European Border and Coast Guard Agency, and of NGOs are truly remarkable."

UPDATE: The #Prudence has taken on a transfer of ~200 #people rescued by @jugendrettet yesterday. pic.twitter.com/nidoSN78wk

— MSF Sea (@MSF_Sea) May 7, 2017

Italy's ruling center-left Democratic Party and the European Commission have also defended the NGOs.

NGOs have rescued about one-third of the more than 43,000 migrants who have made the crossing so far this year. On Friday and Saturday alone, some 6,000 migrants were picked up at sea by NGOs, the Italian navy and Frontex reported.  More than 1,150 migrants have drowned so far this year.

Accusations of collusion

Italian Prosecutor Carmelo Zuccaro has in recent weeks accused some private charity boats of colluding with Libyan traffickers, allegations that have been picked up by some politicians in Italy.

The EU border control agency Frontex in a February report described the NGOs as "unintentionally" acting like a "pull factor" for more crossings by saving migrants close to the Libyan coast. But Frontex says there is no evidence of collaboration between the smugglers and NGOs.

The NGOs, led by SOS Mediterranee and Medecins sans Frontieres (MSF), have defended their actions and denied cooperating with Libyan smugglers. They say they are simply carrying out rescues that should be organized by European governments.

Zuccaro has said bigger charities like MSF and Save the Children were beyond reproach, but he accused smaller private NGO boats of cooperating with smugglers. He has presented no hard evidence to back up the claims, which have since been echoed by Italy's populist Five Star Movement and right-wing Northern League.

Migrants from Africa fleeing war and poverty have created an opportunity for smugglers based in Libya.

War, famine and poverty

The UN said on Monday that war and famine have forced more than two million children in South Sudan to flee their homes.