KABUL (WIREUPDATE.COM) — A loud explosion that shook the southern part of the Afghan capital of Kabul on early Tuesday is believed to have been caused by a suicide car bomber, according to witnesses and officials.

The blast is believed to have happened near a military base outside the center of Kabul, near Darul Aman Palace – a European-style palace built during the 1920s as part of the reformist King Amanullah Khan’s modernization drive. Another report, however, said it happened near the Afghan Parliament.

It was not immediately clear if there were any casualties from the explosion. On normal Tuesdays, the area where it happened is very busy. “I fear there’ll be a lot of casualties,” one witness said. “It’s a very busy time of the morning.”

Violence in the Afghan capital has been lowering over the past year, but Kabul is still the scene of infrequent attacks that sometimes cause mass casualties.