A car bomb exploded early Monday at the gates of Jalalabad airport in eastern Afghanistan, officials said. The number of casualties was not immediately known.
Nangahar provincial spokesman Ahmadzia Abdulzai said he did not yet know how many were dead or injured, but there were casualties. While the blast came from explosives in a vehicle, Abdulzai also said it was not yet clear if it was a parked car that was detonated remotely or a vehicle driven by a suicide bomber into the entrance of the airport.
The blast was "very strong," said provincial police spokesman Hazrad Mohammad. He did not have further details.
An AP photographer saw at least four destroyed cars at the gates of the airport, which serves both civilian and international military aircraft.
The explosion comes after nearly a week of deadly protests in Afghanistan in the escalating crisis over the burning of Muslim holy books at an American military base. More than 30 people have been killed in the violence, including four U.S. soldiers.
Insurgents regularly target government installations in Afghanistan so it was unclear if the Jalalabad attack was in retaliation for the Quran burning.
The blast comes a day after demonstrators hurled grenades at a U.S. base in northern Afghanistan, and a gun battle left two Afghans dead and seven NATO troops injured Sunday in the escalating crisis over the burning of Muslim holy books at an American airfield.
More than 30 people have been killed, including four U.S. troops, in six days of unrest. Still, the top U.S. diplomat in Afghanistan said the violence would not change Washington's course.
"Tensions are running very high here, and I think we need to let things calm down, return to a more normal atmosphere, and then get on with business," Ambassador Ryan Crocker told CNN's "State of the Union."
"This is not the time to decide that we're done here," he said. "We have got to redouble our efforts. We've got to create a situation in which al-Qaida is not coming back."
The attack on the base came a day after two U.S. military advisers — a lieutenant colonel and a major — were found dead after being shot in the head in their office at the Interior Ministry in the heart of the capital. The building is one of the city's most heavily guarded buildings, and the slayings raised doubts about safety as coalition troops continue their withdrawal.
The incident prompted NATO, Britain and France to recall hundreds of international advisers from all Afghan ministries in the capital. The advisers are key to helping improve governance and preparing the country's security forces to take on more responsibility.
A manhunt was under way for the main suspect in the shooting — an Afghan man who worked as a driver for an office on the same floor as the advisers who were killed, Interior Ministry spokesman Sediq Sediqi said. He did not provide further details about the suspect or his possible motive.
The Taliban claimed that the shooter was one of their sympathizers and that an accomplice had helped him get into the compound to kill the Americans in retaliation for the Quran burnings.
Afghanistan's defense and interior ministers were to visit Washington this week, but they called off the trip to consult with other Afghan officials and religious leaders on how to stop the violence, Pentagon press secretary George Little said. The Afghan officials had planned to meet with Defense Secretary Leon Panetta and Joint Chiefs Chairman Gen. Martin Dempsey.
The protesters in Kunduz province in the north threw hand grenades to express their anger at the way some Qurans and other Islamic texts were disposed of in a burn pit last week at Bagram Air Field, north of Kabul.
Protests continue despite apology
President Barack Obama and other U.S. officials have apologized for the burnings, which they said were a mistake. But their apologies have not quelled the anger of Afghans, who say the incident illustrates foreigners' disrespect for their culture and religion.
Last week, during a protest in Nangarhar province in the east, two other U.S. troops were killed when an Afghan soldier turned his gun on them.
In Sunday's protest in Kunduz, thousands of protesters tried to enter the district's largest city. Armed individuals in the crowd fired on police and threw grenades at the U.S. base on the city outskirts, said Amanuddin Quriashi, administrator in Imam Sahib.
Seven NATO troops were wounded by the grenade. One protester was killed by troops firing from the U.S. base, and another was killed by Afghan police, Quriashi said.
A NATO spokesman said an explosion occurred outside the base, but that the grenades did not breach its defenses.
In a televised address to the nation, Afghan President Hamid Karzai renewed his calls for calm. Karzai did not mention the killings at the ministry in his opening remarks but when a reporter asked, he said he was "saddened" by their deaths.
He said the unprecedented recall of advisers was understandable, calling it "a temporary step at a time when the people of Afghanistan are angry over the burning of the holy Quran."
Members of the international military coalition described the removal of advisers as a temporary security measure, stressing that they did not expect it to affect partnerships with the Afghans.
"We continue to move forward and stand by our Afghan partners in this campaign. We will not let this divide the coalition," said Lt. Col. Jimmie Cummings, a spokesman for the international force.
Germany has withdrawn troops early from an outpost in northern Afghanistan because of the Quran protests.
In Berlin, Defense Ministry spokesman Stefan Paris said late last week that the German military, which handed over security responsibility for the Taloqan area to Afghan authorities on Feb. 15, originally planned to shut down its base there altogether in late March. But the regional commander decided to pull the remaining 50 German troops back to a large base in Kunduz because of nearby demonstrations.