Sultan Pradhan, the head of the department of health, said there were no immediate threats to health in the capital, while officials also confirmed that some people were still unable to travel out due to security concerns.

As a result, many people headed to central Sarajevo, which is about 20 kms (12 miles) from the city center.

“We are worried,” a woman named Daudka Muharem said outside her house. “I know if the bomb explodes, it will hit me. I am afraid from the sound of it.”

Officials did not immediately say whether there was a militant link.

“This is a tragedy,” Bosnia’s president, Alija Izetbegovic, said through a statement. “As you understand, more than 500 people were killed and thousands injured in the bombings. This would not have happened if it were not for the hard work of local people who stopped the attack.”

A day into the bombing campaign, the United States said it condemned the attacks but not those that had occurred at home.

The bombings came nearly a year after the United States and other Western powers began a military action in Afghanistan known as Operation Enduring Freedom.

“We condemn all acts of terrorism and seek justice for the victims, and continue to call for an end to the violence,” an official in the U.S. delegation to the talks in Berlin said Friday.

There were conflicting reports about the cause of the explosions. A police source told Bosnia’s private RTVP2 television that they had detonated bombs but could not confirm anyone had died.

“As we can see now, bombs were detonated in several places and explosions shook the city,” RTVP1 reported.

Also on Friday, a Bosnian army helicopter landed at the Sarajevo airport after it mistook a NATO aircraft for one that had been mistakenly bombed during earlier exercises.

The two jets were both on a routine training mission, and no injuries were reported.

But the incident highlights the challenges in dealing with the threat posed by militant groups as the war against Islamist fighters and separatist groups in the south moves closer to home.

“This will not stop us,” Prime Minister Aleksandar Vucic told an event in the eastern city of Gradisk, according to Reuters. “This is a war that has already changed many peoples’ lives…. To