German aid group Sea-Watch said Monday it had resumed its migrant rescue operations in the Mediterranean after a three-month break, when Europe was largely in lockdown over the coronavirus pandemic.

The Sea-Watch 3 rescue vessel had left the Sicilian port of Messina and was on its way towards waters off the Libyan coast, the NGO said on Twitter.

A new boat funded by the German Protestant Church, the Sea-Watch 4, will also set sail for Libya "in a few weeks" from the port of Burriana, near Valencia, it said.

Everyone on board the Sea-Watch 3 underwent a 14-day quarantine and a test for the new coronavirus before the boat's departure from Messina, said the group.

The Sea-Watch 3 will be the first NGO rescue boat operating in the area for more than two months. 

In April, the Alan Kurdi and Aita Mari, two aid boats that had continued to operate despite the coronavirus lockdown across Europe, were detained by the Italian coastguard due to "technical" problems. 

The NGOs said this move was intended solely to disrupt their rescue missions.

Malta and Italy officially closed their ports to migrants in April due to the coronavirus pandemic, a decision heavily criticised by aid groups.

Some 425 migrants who had been picked up during various rescue operations were allowed to disembark in Malta at the weekend after nearly 40 days onboard four tourist boats.

The migrants had been in limbo since April on the chartered boats held outside Maltese waters. 

Malta had refused them entry, saying its ports were closed due to the coronavirus emergency and its detention centres were full.

But in an about-face late on Saturday, Malta's government said it was not prepared "to endanger lives of both the migrants and the crew, due the lack of solidarity shown by European Union member states in terms of relocation". 

Malta had come under fire from humanitarian groups for holding the migrants on the tourist boats, which were not designed for lengthy stays.