MOSCOW/WASHINGTON - Russian President Vladimir Putin and US President Barack Obama agreed in a phone call on Friday that the current standoff in Ukraine serves no one' s interest and said they would keep open their channels of communication.

It was the first conversation between the two leaders since the United States and the European Union slapped a new round of sanctions against Moscow on Tuesday over Russia's alleged involvement in the flare-up of tensions in eastern Ukraine. The fresh package of punitive measures and the July 17 downing of a Malaysian Airlines jet which killed all 298 people aboard further strained the bilateral ties.

"The presidents agreed that the current situation is not in the interests of either country," said a Kremlin statement.

In the phone talk, Putin said Washington's efforts to build up sanction pressure on Russia are counterproductive and detrimental to bilateral relations well as international stability.

"The Russian leader described Washington's course of ramping up sanctions pressure as counterproductive, causing serious damage to bilateral relations and international stability in general," the Kremlin said in a statement.

"Despite considerable differences in assessments of a number of key aspects, both sides stressed that the top priority was to immediately stop hostilities in Ukraine's southeastern regions and launch a political process," the Kremlin said.

As international investigators combed through the crash site, trying to retrieved the remains of the victims and the key pieces of information, heavy fighting between the separatist and Ukrainian troops continued to inflict more casualties.

Obama reiterated his "deep concerns about Russia's increased support for the separatists in Ukraine," and "reinforced his preference for a diplomatic solution to the crisis in Ukraine," the White House said in a statement.

The two leaders agreed to keep open their channels of communication, it added.

They also spoke positively of a meeting that took place the day before in Minsk, Belarus, among members of a diplomatic "contact group" pursuing an end to hostilities, according to the Kremlin statement. That group includes representatives from Russia, Ukraine and the Organization for Security and Cooperation in Europe.

The two presidents stressed the necessity of continuing negotiations in this format, the Itar-Tass news agency quoted the Kremlin as saying.

Over the phone, Obama also "reiterated his concerns about Russia's compliance with its obligations" under a 1987 missile treaty, said the White House.

Obama has written to Putin about US findings over Russia's testing of cruise missiles in violation of the Intermediate-Range Nuclear Forces Treaty which bans ground-launched ballistic or cruise missiles with a range of 500 to 5,500 kilometers. Russia said on Thursday it had been strictly implementing the major arms control deal.

Also on Friday, US Vice President Joe Biden spoke with Ukrainian President Petro Poroshenko on the situation in Ukraine. Biden announced about 8 million US dollars in new assistance to the Ukrainian State Border Guard Service, the White House said in a separate statement.

Poroshenko informed Biden that access to the flight MH17 crash site had been secured on both Thursday and Friday, it said.