WASHINGTON - The US State Department on Thursday vowed to seek "full accountability" for the alleged Quran burning by US troops in Afghanistan, which has touched off deadly violence in the war-torn country.

"We are looking to collaborate with Afghan authorities as we do a careful examination of the facts pertinent to this incident," department spokesman Mark Toner told reporters at a briefing.

"We're certainly going to seek full accountability for the actions of those individuals in burning the Qoran," he added.

Protests in Afghanistan over the alleged Quran burning by US troops in Bagram airbase entered its third day on Thursday, leaving 15 people dead and 59 others wounded across the country.

With violence that is getting out of control, US President Barack Obama was forced to render his apology for the incident. A statement released by the Afghan Presidential Palace on Thursday said: "In the official letter conveyed to the President this afternoon by Ryan Crocker, the US ambassador to Afghanistan, President Obama has written that the incident in their facility was not intentional and assured the President of full investigation."

Admitting that "emotions are running extremely high" in Afghanistan, Toner, again, offered apologies and pledged that his government will "get to the bottom of this."