A suicide bomber has killed himself and a Turkish security guard at the U.S. Embassy in Ankara.
Another person was seriously wounded in what U.S. and Turkish officials described as a "terrorist" attack.
The U.S. State Department said American officials were working with Turkish authorities to investigate the attack that occurred at an entrance of the embassy compound.
There was no claim of responsibility, but Turkish Prime Minister Recep Tayyip Erdogan said the bomber was a member of the Revolutionary People's Liberation Party-Front.
The far-left group has claimed responsibility for a number of deadly attacks since the 1970s.
The State Department warned American citizens “to be alert to the potential for violence, to avoid those areas where disturbances have occurred and to avoid demonstrations and large gatherings."
In comments broadcast on television, Turkish Prime Minister Recep Tayyip Erdogan called for a global effort to combat "terrorist elements."
The explosion damaged the compound's outer wall, blowing out the concrete around a door to the street.
Shortly after the blast, U.S. Ambassador Francis Ricciardone told journalists: "Right now we are all dealing with our sadness at the loss of our fellow member of our embassy. We salute his bravery, his service to Turkey and to Turkish-American friendship. Our hearts go out to his family."
Interior Minister Muammer Guler said a Turkish woman was badly wounded in the attack and that two security guards were receiving outpatient care at a hospital.
Leftist activists, along with Kurdish rebels and Islamic militants, have launched attacks in recent years in Turkey.
A 2007 attack in Ankara that killed nine was blamed on a leftist suicide bomber.
With reporting by Reuters, AP, and AFP