NATO said Tuesday it has seen no sign of a Russian troop withdrawal from the border with Ukraine after Moscow insisted it would not invade its Soviet-era satellite.

"We currently have no information that indicates a withdrawal of Russian troops from the Ukrainian border," a NATO official said.

"We continue to urge Russia to abide by the Geneva agreement and to pull back all its troops along the Ukrainian border in favour of diplomacy and dialogue," the official, who spoke on condition of anonymity, said.

On Monday, the Pentagon said US Secretary of Defense Chuck Hagel had spoken by telephone with his Russian counterpart Sergei Shoigu and that "Shoigu reiterated his assurance that Russian forces would not invade Ukraine."

Hagel and Shoigu discussed a range of issues related to the situation in Ukraine, a statement said, with Hagel requesting clarification of Russia's intentions as it has massed an estimated 40,000 troops on the border.

In Moscow's version of the exchange, Shoigu told Hagel that troops had returned to barracks after conducting exercises.

"Russia was forced to launch large-scale exercises near the border with Ukraine, facing the prospect of (Ukrainian) military action against civilians," Shoigu said.

"Once the Ukrainian authorities declared that they would not use regular military units against the unarmed population, the Russian troops returned to barracks."