Ukraine crisis: Pentagon says Russian jets violated airspace --- The US says Russian military aircraft have entered Ukrainian airspace on several occasions, amid rising tension in the east of the country. -- A Pentagon spokesman called on Russia to "de-escalate the situation". -- The statement came as the G7 group of industrialised countries agreed on Saturday to "swiftly" impose fresh sanctions on Russia over Ukraine. -- Meanwhile, talks are under way to secure the release of international observers seized by separatists. -- Russia has tens of thousands of troops deployed along its side of the border with Ukraine as pro-Moscow separatists continue to occupy official buildings in a dozen eastern towns, defying the government in Kiev. --- Russia has accused the West of wanting to "seize" Ukraine. --- In a statement on Friday, Pentagon spokesman Col Steven Warren said Russian aircraft had entered Ukrainian airspace several times in the past 24 hours. -- He gave no further details, but called on Moscow to take "immediate steps to de-escalate the situation". -- US Secretary of Defense Chuck Hagel earlier described Russian activity along the Ukrainian border as "dangerously destabilising" and "very provocative". - BBC, at: http://www.bbc.com/news/27167187