WASHINGTON, July 28. / ITAR-TASS /. US Secretary of State John Kerry asked Russia to stop the flow of heavy weapons to Ukraine. He said this during a telephone conversation with Russian Foreign Minister Sergei Lavrov.

"Secretary of State urged Lavrov to stop the flow of heavy weapons, rockets and artillery from Russia to Ukraine and to begin to contribute to de-escalating the conflict. He did not accept Lavrov’s denial that heavy weapons from Russia were contributing to the conflict," the State Department statement said.

Earlier, Russian Foreign Minister Sergei Lavrov asked the United States to stop hindering the work of the Organization for Security and Cooperation in Europe (OSCE).

Lavrov stressed that “Russia invited OSCE observers to its border checkpoints Gukovo and Donetsk at the border with Ukraine and expects they will arrive without delays,” the ministry said. “He asked John Kerry to instruct his subordinates not to hinder the OSCE in its work.

Lavrov and Kerry agreed that despite all the differences in their approaches to the settlement of the Ukrainian conflict it was vital to press towards for the immediate ceasefire and the launch of talks between the conflicting parties in line with the agreements committed to paper in the Geneva communique signed by Russia, the United States, the European Union and Ukraine on April 17, 2014.

Apart from that, the two foreign ministers exchanged views on the situation in the Middle East, where the US Secretary of State had been on a working visit on Saturday. They also discussed the situation in the bilateral dialogue on non-proliferation problems.