At least nine people died when an overcrowded migrant boat capsized off the coast of Libya and 144 more were rescued, the Italian coast guard said on Monday, after another heavy weekend for maritime rescue services operating off North Africa.

A spokesman for the Italian coastguard said 5,629 people were rescued from 22 different vessels in the three days between April 10-12. Vessels and aircraft from the Italian coast guard and navy as well as merchant ships and an Icelandic patrol boat assigned to the European Triton border protection operation were involved.

Rescue services were alerted on Sunday afternoon about the boat that capsized some 80 miles north of the Libyan coast. Nine bodies were recovered and were being brought to shore on Italian coast guard and navy vessels.

Around 3,500 people are estimated to have drowned and 170,000 reached Italy as the migrant crisis has intensified with continuing instability in Libya, the staging point for most of the boats trying to cross to Sicily.

The number of boats carrying migrants aiming to reach the European Union from Africa has picked up in recent weeks as fine spring weather has made the passage safer. In February, more than 300 drowned when attempting the crossing in cold weather and rough seas.

At least 480 migrants died in the Mediterranean in the first three months of 2015, compared with fewer than 50 in the same period last year, the International Organization for Migration said on Friday.

Around 3,500 are estimated to have drowned last year when more than 170,000 migrants managed to reach Italy by sea.