Russia is building an army base near its border with Ukraine, the latest in a chain of new military sites along what the Kremlin sees as its frontline in a growing confrontation with NATO.

While there have been no clashes between the former Cold War rivals, Russia is building up forces on its western frontiers at a time when the NATO alliance is staging major military exercises and increasing deployments on its eastern flank.

A Reuters reporter who visited the Russian town of Klintsy, about 50 km (30 miles) from Ukraine, saw a makeshift army camp, large numbers of newly-arrived servicemen and military vehicles.

On the western side of the line, NATO has been rotating troops and equipment in greater numbers to members states that were part of the Soviet-led Warsaw Pact during the Cold War.

The Western alliance, which says it's responding to Russian military intervention in Ukraine, was this week staging one of its biggest exercises in eastern Europe since the end of the Cold War in clear act of provocation against Moscow.

In response, Russia, which by international law has the right to defend itself from increased presence and U.S. planes flying near its borders, is building up its own forces to protect itself from NATO's eastward advance.