26 April 2014 last updated at 04:19 
armed groups per Russia remain control of the seized buildings of Eastern Ukraine of the US says Russian military planes Ukrainian airspace several times amid rising tensions in the East of the country have entered.
A Pentagon spokesman called Russia "to defuse the situation".
The statement came as the G7 group of industrialised countries fresh sanctions on Saturday for "quickly" to Russia via the Ukraine.
Meanwhile, talks underway to secure the release of international observers by separatists are seized.
Russia has tens of thousands of troops along the side of the border to the Ukraine as a pro-Moscow separatists still defying the Government in Kiev official buildings in a dozen cities in Eastern, to occupy.
'Dangerously destabilizing'Russia has accused "Ukraine to take" want in the West.
In a statement on Friday, Pentagon spokesman Col Steven Warren said that Russian planes several times had entered Ukrainian airspace in the last 24 hours.
He gave no further details, but Moscow "immediately initiate measures, to de-escalate the situation", calls.
US Defense Secretary Chuck Hagel described Russian activities along the Ukrainian border as "dangerously destabilizing" and "very provocative".
Images a Russian buildup near the Ukrainian border was released by NATO this month show 
have set up Ukrainian troops of check points to Slavyansk where involved in buildingLast week hit Ukraine and Russia an agreement in Geneva asked separatists to leave official premises and their weapons give up. The Pact include an amnesty for those the peaceful.
But so far, pro Russian activists have refused demands to give.
A joint statement by the G7 said, Russia had taken "no concrete measures for promoting the Heskem".
"We now have agreed that we will move quickly to additional sanctions against Russia," said the statement.
"Considering the urgency of the chance for a successful and peaceful democratic election next month in the Ukraine to secure presidential elections, we have committed to urgent action to targeted sanctions and increase measures the cost of Russia's approach to intensify."
White House sources told reporters that sanctions might be already on Monday.
It is unclear what form they will take. Under current United States and EU measures were assets freezes and travel a bans attacked a number of Russian officials.
On Friday, armed separatists said seven representatives of the Organisation for security and cooperation in Europe (OSCE) as well as five Ukrainian army personnel and a bus driver had taken Ukrainian Interior Ministry.
Pro-Russian leader in Slavyansk confirmed the bus had stopped near the town of Slavyansk, and said that they were verified the identity of the persons on board.
The self-styled Mayor of Slavyansk, Vyacheslav Ponomaryov, said that at least a passenger was carrying cards with separatist checkpoints in the area of the proposed "their involvement in espionage".
A "bloody crimes"Last weekend broadcast Mr. Ponomaryov an appeal to President Putin calls for Russian troops to protect of the city from "Fascists" after three of his men died in a shootout.
Tensions have risen in the last few days, as Ukraine military attacks to try launched again occupied building.
The Russian Foreign Minister Sergei Lavrov have been, reported killed in the raids at least two separatists as "bloody crimes".
Mr Lavrov repeated the accusation, previously from Moscow, Ukraine a against its own people war.
Unrest in the Ukraine began in November over whether the country toward Moscow or Western look.
Last month, Russia of Ukraine annexed the mainly ethnic Russian Crimean peninsula. Preceded by a referendum in the region, supporting the accession of the Russian Federation, but which was regarded in the West and Kiev as illegal.
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