Jim Michaels

USA TODAY

The United States released a series of satellite images Sunday that appear to support its claims that Russian forces have fired across the border into Ukraine to support rebels there, suggesting a new level of direct Russian involvement in the conflict.

The images show artillery and rocket-blast signatures inside Russia and craters formed by the artillery strikes in Ukraine.

Washington has accused Russia of arming, training and financing separatists in Ukraine.

The images were provided by a senior intelligence official who asked not to be named in order to discuss intelligence issues. The images were also distributed by State Department officials.

The images were dated in recent days, though it was not clear when the artillery strikes were launched.

One image shows a Ukrainian military position July 20 and the same area July 23 with numerous craters made by an artillery barrage, indicating the strike took place sometime between those dates.

The recent activity suggests that Russia has continued to support separatists, even though Russian-backed separatists have been accused of shooting down the Malaysia Airlines flight on July 17, drawing international condemnation.

The U.S. said Russia has been bolstering support to separatists in eastern Ukraine to counter progress that Ukraine's armed forces have made against the rebels.

On Sunday, Ukraine's National Security Council said government troops have encircled Horlivka, a key rebel stronghold near where the airliner crashed, and there had been fighting in other cities in the east, the Associated Press reported. Horlivka is about 20 miles north of the main rebel-held city of Donetsk.

Analysts say the firepower and anti-aircraft weapons from Russia provide the rebels with a critical edge in their battle against Ukraine's government forces.

The rockets can be fired at troop formations, air fields, staging areas, artillery positions and other "area targets," said Jim Howcroft, a retired Marine intelligence officer with extensive experience in the region. He said that capability would allow rebels to break up offensives launched by Ukrainian forces.