An explosion ripped through the security point outside of the United States Embassy in Ankara shortly after noon on Friday, according to a statement issued by US State Department spokeswoman Victoria Nuland.

"One of our direct-hire local guards was killed," Nuland said. "We offer our deepest condolences to his family."

"The guard who was there, (on) his side of the security barrier was killed, but two who were in that same building, but on the other side of the glass survived," Nuland said.

"We had a Turkish visitor who is in serious condition," Nuland said, adding that the visitor is believed to be a well-known journalist. No Americans appeared to have been injured in the attack.

The suicide bomber was killed in the blast.

"We are working closely with the Turkish national police to make a full assessment of the damage and the casualties, and to begin an investigation," Nuland said and stressed that "the level of security protection at our facility in Ankara ensured that there were not significantly more deaths and injuries."

Both US and Turkish officials classified the attack as an act of terrorism.

In the hours that followed, the US State Department issued a security warning on its website. US citizens in Turkey were advised to avoid other consulates and any areas where violence had previously occurred.

Turkey: 'We will stand together'

The cause of the attack remained unclear into the evening on Friday. Officials from both countries announced they would work together to uncover the motive and any remaining suspects linked to the explosion.

"The attacks target the well-being and peace in our country," Prime Minister Recep Tayyip Erdogan said on television. "We will stand tall and we will stand together ... We will get over this."

Interior Minister Muammer Guler told reporters that the government suspected a member of a far-left group was behind the attack.

Early reports suggested that the bomber had been linked to the Revolutionary People's Liberation Party-Front (DHKP-C), a group that has been blamed for acts of terror against the Turkish government since the 1970s. Two weeks ago, police arrested dozens linked to the group in a nationwide raid.

A range of groups, including right- and left-wing extremists, Kurdish separatists and Islamist militants, have carried out attacks on Turkish soil over the years.

The US and Turkey are strong NATO allies. Most recently, the US government has deployed Patriot missiles to the Turkey-Syria border in an effort to help Ankara protect itself from the threat of violence spilling over from the civil war across the border.

NATO Secretary General Anders Fogh Rasmussen released a statement Friday condemning the attack: "I strongly condemn today's bomb attack on the embassy of the United States in Ankara, which killed and injured a number of people."

"This is an outrageous attack on the diplomatic premises of one ally, on the territory of another ally," he said. "It shows a reckless disregard for human life and for the inviolability of diplomatic staff."

The last attack on a US mission in Turkey occurred in 2008, when several gunmen killed three police officers at the consulate in Instanbul.

kms/hc (AFP, AP, dpa)