WASHINGTON (AFP) - Attacks on the police and security service buildings in eastern Ukraine by pro-Russian gunmen bore "telltale signs of Moscow's involvement", the United States envoy to the United Nations said on Sunday.

Speaking on ABC television's "This Week" programme, Ambassador Samantha Power dismissed suggestions that the attacks, which have triggered gun battles with Ukrainian special forces, were the work of grassroots militia groups.

"It's professional, coordinated. Nothing grassroots about it," Ms Power said. "The forces are doing in each of the six or seven cities they have been active in exactly the same thing. So, certainly, it bears the telltale signs of Moscow's involvement."

At least two people were killed and nine wounded in fighting on Sunday that has threatened to scupper the first international talks on the worst East-West crisis since the Cold War.

The clashes across the former Soviet state's separatist eastern rust belt broke out a day after masked gunmen stormed a series of police and security service buildings in coordinated raids that Kiev blamed on the "provocative activities of Russian special services".

It was the latest development in a crisis that has escalated since Western-backed leaders rose to power in February on the back of bloody protests against the old regime's decision to reject an alliance with the European Union and look for future assistance from the Kremlin.