Updated

Greek police detained dozens of people Thursday during a protest at the merchant marine minister's office over the deaths of immigrants whose boat sank as it was being towed by the Coast Guard.

Twelve people, mostly children, are believed to have died last week when a small boat carrying 28 people from Turkey into Greece sank in the eastern Aegean Sea. Only two bodies, those of a woman and a child, have been recovered.

Police detained 47 people during the protest at office of the minister, Miltiadis Varvitsiotis, who is responsible for the Coast Guard.

Police said the protesters broke windows, wrote slogans on walls and put up posters. One was later arrested for allegedly swearing at police and resisting the detention process.

The youth wing of the left-wing main opposition Syriza party accused police of brutality, saying their protest was peaceful and that there was no reason for police to respond forcefully.

The sinking has led to an increasingly heated political debate in Greece, with the government — and Varvitsiotis in particular — coming under criticism. Authorities have ordered an investigation into the accident.

Survivors have said the Coast Guard boat was towing their vessel back into Turkish waters to be abandoned, and that the crew didn't help passengers struggling in rough seas after their boat sank. The Coast Guard has rejected the criticism, saying it was towing the boat to the nearby Greek island of Farmakonisi when the accident occurred, and that the crew rescued as many people as they could.

International rights groups have been calling for an investigation into whether the Coast Guard was engaging in a policy of pushbacks, under which migrants trying to enter Greece illegally are forcibly pushed back out of Greek borders without having a chance to apply for asylum.

"Members of Greece's parliament should urgently establish an inquiry into all allegations of collective expulsions, pushbacks, and dangerous maneuvers by the Greek Coast Guard on Greece's sea borders with Turkey," the rights group Human Rights Watch said Thursday.

"Despite government denials, we've heard many accounts of pushbacks that put migrants' lives at risk," Eva Cossé, Greece specialist at Human Rights Watch, said in a statement.