He said it seemed to have ‘‘very deep roots’’ and means of recruitment in several urban centers, including Istanbul, Ankara and possibly the coastal city of Izmir. Jeffrey said it was unlikely the attack was a response to recent regional developments — including, for example, Israel’s strike this week on a Syrian target — but did not rule out that DHKP-C conducted the bombing as a kind of subcontractor for another group.
He also said the embassy’s strong defenses worked as they were supposed to, with the ‘‘minimum number of casualties’’ for such a grave attack.
‘‘It’s a very hard perimeter to crack, as we saw today,’’ Jeffrey said.
In past years, the DHKP-C group has spearheaded hunger strikes against Turkish prison conditions that led to the deaths of dozens of inmates. The protesters opposed a maximum-security system in which prisoners were held in small cells instead of large wards.
In September, police said a leftist militant threw a grenade and then blew himself up outside a police station in Istanbul, killing a police officer and injuring seven others. Police identified the bomber as a member of the DHKP-C.
In 2008, Turkish police said they had foiled a bomb plot by DHKP-C against some U.S. companies in Turkey.
Turkey has also seen attacks linked to homegrown Islamic militants tied to al-Qaida. In a 2003 attack on the British consulate in Istanbul, a suspected Islamic militant rammed an explosive-laden pickup truck into the main gate, killing 58 people, including the British consul-general.
Associated Press writers Ezgi Akin in Ankara, Turkey, Christopher Torchia in Istanbul, Nedra Pickler and Bradley Klapper in Washington, Raf Casert in Brussels, and Cassandra Vinograd in London contributed to this report.