The US ambassador in Kiev Geoffrey Pyatt has waded into the debate about Russia's intentions with Ukraine by tweeting a photo reportedly showing the build-up of Russian troops on the border of ex-Soviet Republic.

The tweet, with the English words "proof of RU military buildup", shows three successive photos of a field in Rostov-on-Don, Russia taken in October last year, March and April.

The first photo shows an empty field, while in the March photo there are arrays of armoured vehicles. In the final photo, dated April 2, the field is densely packed with what appear to be vehicles and tents.

— Geoffrey Pyatt (@GeoffPyatt) April 9, 2014

The images come as Russia and the West tussle over Moscow's intentions for the rest of Ukraine, following its annexation of the eastern region of Crimea in March.

Russia claims the presence of its troops over the border are no reason to worry, even as US diplomats point to what they claim is Russian interference within eastern Ukraine. Western leaders say the Russian activity mimicks its actions before Russia annexed Crimea, triggering the worst East-West crisis since the end of the Cold War in the early 1990s.

As Kiev’s interim leaders pledge to clear the Russian protests occurring in the eastern part of Ukraine, Russia has warned against making irreversible mistakes. Russia, Ukraine, the EU and the US are due to begin negotiations on a diplomatic resolution in Vienna on April 17.

NATO meanwhile has denied intentions to deploy massive amounts of troops near the Russian border.