The Italian coastguard said that 1,725 migrants were rescued off the Libyan coast Thursday, bringing the total number saved since Sunday to at least 14,000.

Those plucked from the Mediterranean Thursday were on 16 small boats, mostly dangerous inflatables, and were rescued by Italian naval vessels, ships from the EU's "Sophia" anti-trafficking mission, NGO boats and two passing merchant ships, the coastguard said.

Good summer weather has caused spike in attempted migrant crossings, including a record 6,500 people picked up on Monday. Three people were found dead on a boat on Wednesday, the coastguard said.

Italy is sheltering growing numbers of would-be refugees as its neighbours to the north move to tighten their borders and make it harder for migrants to travel to their preferred destinations in northern Europe.

According to the interior ministry, Italy now has 148,000 asylum seekers in reception centres, compared with 103,000 in 2015 and 66,000 in 2014.

Despite the large numbers arriving in recent days, the total number of new arrivals so far this year remains similar to 2015, with 116,149 migrants registered by the Italian authorities from January to August.

Nearly all are from sub-Saharan Africa.

Italian Prime Minister Matteo Renzi and German Chancellor Angela Merkel agreed Wednesday to step up efforts to send migrants with no right to asylum in Europe back to their homelands.