Obama concerned over Koran burning President Barack Obama holds a press conference in the Brady Press Briefing Room at the White House in Washington, March 6, 2012. WASHINGTON, March 7 (UPI) -- U.S. President Barack Obama warned the inadvertent Koran burning in Afghanistan that led to deadly protests is an "indication of the challenges" there. Addressing a news conference at the White House Tuesday, the president expressed concerns about the violence stemming from the Koran burning by U.S. troops Feb. 20. Dozens of Afghans and at least six U.S. soldiers have died since the incident despite apologies from Obama and the NATO commander. "I think that it is an indication of the challenges in that environment, and it's an indication that now is the time for us to transition," the president said, but added violence directed at coalition forces is unacceptable. "We're going to be able to find a mechanism whereby Afghans understand their sovereignty is being respected and that they're going to be taking a greater and greater role in their own security," Obama said. That, I think, is in the interests of Afghans. It's also in our interests. And I'm confident that we can execute but it's not going to be a smooth path. There are going to be bumps along the road, just as there were in Iraq," he said. Obama said Afghan President Hamid Karzai "understands that we are interested in a strategic partnership with the Afghan people and the Afghan government." The president said the United States is not interested in staying in Afghanistan "any longer than is necessary to assure that al-Qaida is not operating there and that there's sufficient stability that it doesn't end up being a free-for-all after (International Security Assistance Force) has left." Obama reminded the transition policy calls for turning over increasing responsibility to Afghans and a "full transition so that our combat role is over by the end of 2014."