TUNIS, Aug 23 (Reuters) - Eleven bodies have been recovered by Tunisia's coastguard after a boat carrying Tunisian migrants sank at the weekend en route to Italy, with three others still unaccounted for, the National Guard said on Sunday.

Coastguard, military and civil protection teams, backed by two helicopters, continued to search for the missing.

The boat, which set off early on Thursday with 15 mostly young people on board, sank off the Tunisian coast, and so far only one person was rescued alive, the head of a migrant rights group said on Saturday.

The man who survived said he had been adrift at sea for 48 hours before being rescued by a commercial vessel.

Among those on board were seven members of the same family and a man with his pregnant wife, the head of the Tunisian Observatory for Human Rights told Reuters.

All of the migrants were from the Ben Guerdane area in southeastern Tunisia, and dozens of young people gathered late on Saturday in the town near the Libyan border to demand that search operations be accelerated.

Police fired teargas to disperse the protesters.

The central Mediterranean route from the North African coast is one of the world's deadliest migration routes, used by migrants from Africa and the Middle East seeking to reach Europe, often in overcrowded or unseaworthy boats.

Human Rights Watch, Amnesty International and dozens of other human rights and humanitarian groups said in a statement last month that a migration agreement between Tunisia and the European Union had fuelled and normalised serious abuses against migrants and asylum seekers in Tunisia.

The groups called on the EU to suspend funding for migration and border-control activities involving Tunisian security forces.

(Reporting By Tarek Amara;Editing by Emelia Sithole-Matarise, Tomasz Janowski and Helen Popper)