The Satellite Sentinel Project started by Hollywood star George Clooney said satellite imagery showed six large craters, each approximately 16 meters (52 feet) across, at the Yarmouk military factory in the Sudanese capital Khartoum.

The weapons plant exploded and caught fire shortly after midnight on Wednesday. The SSP said craters at the scene of the explosion were consistent with the kind of damage created upon impact by by air-delivered munitions.

Satellite images made less than two weeks before the blast showed that 40 shipping containers had been stacked next to a shed-like building at the location, according to the SSP, which said those images were "consistent with the presence of highly volatile cargo in the epicenter of the explosions."

"If the explosions resulted from a rocket or missile attack against material stored in the shipping containers, then it was an effective surgical strike that totally destroyed any container that may have remained," said the group, which did not say who it believed was responsible for the strike.

"The explosions destroyed two buildings and heavily damaged at least 21 others, all within 700 meters of the epicenter," the SSP continued in its statement.

"Visible damage includes roof panels blown off and scattered around the area, windows blown out, and walls knocked down," it said, adding that the shed appears to have been completely "pulverized" in the blast.

The SSP, which conducts monitoring of the border between Sudan and South Sudan, aims to deter and document war crimes and crimes against humanity.

The group says its goal is to systematically monitor and report on potential global security hotspots in real-time, relying on satellite imagery, data analysis and sources on the ground. It has documented violent attacks, atrocities and mass graves in Sudan.

The SSP was founded in December 2010 by Hollywood actor Clooney -- an outspoken activist on the violence in Sudan -- and John Prendergast, once a member of former US president Bill Clinton's national security team and one of the founders of the Enough Project, which aims to end genocide and crimes against humanity in conflict-ridden areas of Africa.