WASHINGTON - US Secretary of State Hillary Clinton on Sunday defended President Barack Obama's apology to the Afghans over the burning of Quran by American soldiers, as angry protests ensuing are continuing in the South Asian nation.

"It was the right thing to do to have our president on record as saying this was not intentional, we deeply regret it," Clinton said in Morocco in an interview with CNN.

"I find it somewhat troubling that our politics would enflame such a dangerous situation in Afghanistan," Clinton said of the complaints by Republican presidential candidates and some experts about Obama's apology.

Obama apologized on Thursday in a letter to Afghan President Hamid Karzai over the burning of Quran at the US-run Bagram Airbase near Kabul. The unprecedented anti-US demonstrations in Afghanistan since Tuesday have resulted in over 30 deaths and more than 200 injuries, including four American servicemembers killed in apparent revenge attacks.

"The error was inadvertent," Obama said in his letter to Karzai. "I assure you that we will take the appropriate steps to avoid any recurrence, to include holding accountable those responsible."

"We are hoping that voices inside Afghanistan will join that of President Karzai and others in speaking out to try to calm the situation," Clinton told CNN, stressing that "It is out of hand and it needs to stop."

Washington and its allies, seeking to exit from Afghanistan by 2014, have been aiming at reconciliation talks with the Taliban.