(QHA) -

President of Ukraine Petro Poroshenko in a telephone conversation with the US Vice-President Joseph Biden proposed the United States to join the Ukrainian and international humanitarian mission to Luhansk -- a stronghold for pro-Russian separatists -- under the auspices of the International Committee of the Red Cross, presidential website said Saturday.

Poroshenko emphasized that the mission is possible only if it is an unarmed international team entering the country through Kyiv-controlled border checkpoints.

A White House statement said Biden and Poroshenko agreed that if "Russia were serious about improving the humanitarian situation in eastern Ukraine," it had to immediately stop shelling Ukrainian troops, release Ukrainian hostages being held inside Russia and cease providing weapons to the separatists.

Russia has repeatedly called for a humanitarian mission to be sent into eastern Ukraine. However, Kiev and Western leaders are concerned that any aid mission could be used as a pretext for Russia to send in troops.

U.S. and NATO leaders have claimed that approximately 20,000 Russian forces have massed near the border between Russia and Ukraine. Moscow has denied the Western claims.