ISTANBUL — A man approached a visitor’s gate at the US Embassy in the Turkish capital, Ankara, Friday afternoon and detonated an explosives-packed vest, killing himself and a Turkish security guard, blowing a gaping hole in the wall, and raising new fears about the protection of US diplomats serving in this region.

Within hours Turkish authorities blamed the attack on a homegrown Marxist organization, and Friday evening Prime Minister Recep Tayyip Erdogan said the issue had ‘‘pretty much been clarified’’ because the bomber had been identified, by a skin mark on his head, as a former prisoner once incarcerated for domestic terrorism. Erdogan said DNA testing was underway and would be announced Saturday.