KIEV, Dec. 23 – Russian howitzers and rocket launchers regularly pounded Ukrainian positions across the border in the early stages of the war in eastern Ukraine, AP reported, citing an analysis of hundreds of attack sites published by the open source investigative group Bellingcat.

The 43-page report published last week adds to the pile of evidence suggesting the still-smoldering conflict pitting the Ukrainian government against separatist forces in eastern Ukraine was stage-managed from Moscow — a charge the Kremlin has denied.

"This was an intentional and large-scale attempt to destroy Ukrainian military units that were cutting off separatist supply lines," one of the report's authors, Sean Case, said in a telephone interview.

Russian officials did not immediately return messages seeking comment.

Bellingcat's investigation matched up satellite imagery to a military forensic technique known as "crater morphology."

Traditionally used in the field by soldiers seeking to determine the direction of incoming fire, crater morphology uses the geometry of craters and the pattern of debris ejected by exploding shells to draw lines back to the guns that fired them. Tracing the trajectories from thousands of craters in Ukraine back into Russian territory, the investigators documented more than 500 burn marks from outgoing fire — including the distinctive comet-shaped scorches left by multiple rocket launchers. In many cases, the images showed tracks left by vehicles and, sometimes, Russian artillery positions with guns pointing toward the Ukrainian border.

The investigators said the evidence showed that Russian artillery was used against Ukrainian forces a minimum of 149 times during the summer of 2014 — a critical period during which the Ukrainian military came close to cutting the rebels off from the Russian border before being thrown back by a withering counteroffensive.

Case, a former environmental science student who produced the report with the help of a pseudonymous co-author, describes the 149 figure as conservative. The comprehensive figure, the report said, would most likely be higher.

Bellingcat's analysis struck independent experts as credible.

Sean O'Connor, the principal imagery analyst with IHS Jane's, said in an email that the work looked "solid."

Jonathan Drake, the senior imagery analyst at the American Association for the Advancement of Science, said he had used similar techniques to identify artillery strikes carried out by Sri Lankan government forces in 2009. He called Bellingcat's work impressive and said the over-and-over-again overlap between the geometry of the craters in Ukraine and the orientation of the firing positions in Russia left little doubt about the group's conclusions.

"What you've got there are two independent observations that are consistent with one another and that are consistent over a pretty broad swathe of territory," Drake said in a telephone interview.

Bellingcat's report provides more support for the argument that Russian forces are intimately involved in the fighting in eastern Ukraine, a conflict that pits separatist fighters against the central government in Kiev and has claimed at least 9,600 lives since it broke out in April 2014.

Although the Kremlin acknowledges that many Russians have fought in Ukraine as volunteers, it firmly denies sending its troops across the border or arming the rebels — let alone shelling Ukrainian troops from its territory. Moscow has accused Ukrainian forces of firing into its territory. (ap/ez)