US Vice President Joe Biden has told Ukraine President Petro Poroshenko that the United States was working with European leaders on further sanctions on Russia, over the escalation of the conflict in Ukraine.
"The leaders discussed Russia's ongoing support for the separatists and apparent escalation" the White House said in a statement about the call between the two men.
"The vice president told President Poroshenko that the United States was engaging with European leaders to discuss the imposition of costs on Russia for its continued escalation of the conflict," it said.
Russia said it has invited monitors from the OSCE European security and rights body to two of its borders crossings with Ukraine, as a "sign of good will", the foreign ministry said.
In connection to the worsening situation in the region where Kiev is carrying out its military operation in the southeast of Ukraine, the Russian side, in the order of goodwill and without waiting for a ceasefire is inviting OSCE observers to check points... on the Russian-Ukrainian border.
Russia has been building up its forces on the Ukrainian border steadily over the past few weeks and now has an estimated 10-12,000 troops in the area, a Nato military officer said.
Russia had withdrawn the majority of the 40,000 troops it had on the border earlier this year, and there were fewer than 1,000 by the middle of June. Speaking on the condition of anonymity, the officer told Reuters:
"Our current assessment is that between 10,000 and 12,000 troops are now in the area ... In the last week alone, we have seen several units moving into the border region."
German Chancellor Angela Merkel and Russian President Vladimir Putin agreed that the Ukraine situation "has a tendency towards degradation" and have urged greater peace efforts, Putin's spokesman Dmitry Peskov has said.
He said: "Both Putin and Merkel stressed the necessity to urgently resume the work of a contact group on Ukraine.
"It is their common opinion that, in order for the contact group to resume its work, a ceasefire needs to be declared as soon as possible," Peskov said.
The two leaders met briefly before the World Cup final in Brazil.
Russian President Vladimir Putin could meet his Ukrainian counterpart Petro Poroshenko on the sidelines of the World Cup final in Brazil, although no talks were being planned at this point, a spokesman for the Kremlin has said.
"We are not preparing any separate meetings. As far as we know, he is going there too," said Kremlin spokesman Dmitry Peskov in the Argentine capital Buenos Aires.
"There will be some separate room for leaders at the stadium, and therefore one of course cannot rule it (meeting) out," he said on the sidelines of a meeting between Putin and Argentina's president, Cristina Fernandez.