KABUL - An explosion rocked Bagram Airfield, the main US and NATO base, in Afghanistan's eastern province of Parwan early on Saturday, leaving casualties, the NATO-led Resolute Support said.

"We can confirm that there was an explosion at Bagram Airfield this morning just after 5:30 a.m. (local time). There have been casualties," it said in a statement.

The nature of the blast and further details about the incident remained unknown.

"Our Force Protection and Medical teams are responding to the situation. As we get more information, we will release it," the statement read.

The Bagram Airfield, some 50 km north of Afghan capital of Kabul, has been serving as a main U.S. military base in Afghanistan over the past 15 years.

More than 13,000 NATO-led Resolute Support mission, with majority of them Americans, are stationed in Afghanistan following the end of the combat mission of the alliance forces in the war-torn country in late 2014.