More than 60 migrants of sub-Saharan origin have been lost at sea off Tunisia since Saturday, after two Europe-bound boats sank, local authorities said.
Tunisia and neighbouring Libya are key departure points for migrants who attempt the dangerous crossing from the North African coast to Europe, particularly Italy.
So far this year more than 880 migrants have died trying to reach Europe from North Africa, the International Organisation for Migration says.
Since the start of summer, the number of crossings has increased as migrants take advantage of the good weather and calmer seas, but the number of those lost at sea has also risen.
The Tunisian coastguard retrieved the bodies of 21 migrants after their boat was shipwrecked on Sunday off the port city of Sfax, authorities said on Monday.
"Twenty-one bodies of migrants were recovered after their boat was shipwrecked on July 4, and 50 were rescued," National Guard spokesman Houcem Jebabli told AFP on Monday.
Mr Jebabli said the migrants, all from sub-Saharan Africa, had been trying to reach Europe.
On Saturday, the Tunisian Red Crescent reported that 43 migrants were missing when a boat carrying more than 120 sank off the south-eastern coast near Zarzis.
Tunisia's Defence Ministry said 84 were rescued from the stricken vessel, which the Red Crescent said had set off from Libya's coast.
The National Guard said on Monday that four boatloads of migrants had sunk since June 26 after setting off from Sfax, with 49 bodies recovered and 78 people rescued.
The number of migrants leaving Tunisia for European shores last year hit its highest level since 2011.
In the first three months of 2021, more than half of those arriving in Italy from Tunisia were from sub-Saharan African countries, Tunisian rights organisation FTDES said.
The number of migrants trying to cross from Libya surged to 11,000 between January and April this year, the UN refugee agency said.
The UNHCR said "deteriorating" conditions of migrants in Libya and Tunisia were pushing many to risk their lives on the crossing.
The migrant rescue ship Ocean Viking has rescued 203 people, including 67 children, in recent days, its owner SOS Mediterranee said on Sunday.
The migrants came from Egypt, Gambia, Libya, South Sudan, Syria and Tunisia, the non-government organisation said on Twitter.
A UN Human Rights Office report in late May urged Libya and the EU to overhaul their search and rescue operations in the Mediterranean.
It found that existing policies "fail to prioritise the lives, safety and human rights" of people trying to cross from Africa to Europe.
