WASHINGTON (AFP) - The United States plans to expand military cooperation with Poland and Baltic states to show "support" for its allies after Russia's intervention in Ukraine, Pentagon chief Chuck Hagel said on Wednesday.

"This morning the Defence Department is pursuing measures to support our allies," including expanded aviation training in Poland and increasing the US role in Nato's air policing mission over Baltic countries, Mr Hagel told lawmakers.

At the same hearing, General Martin Dempsey, the US military's top officer, said he had spoken to his Russian counterpart, General Valery Gerasimov, earlier on Wednesday, urging "restraint."

Mr Hagel also said Nato's top commander and head of the US European Command, General Philip Breedlove, planned to confer with Central and Eastern European defence chiefs.

"This is a time for wise, steady, and firm leadership," Mr Hagel told the Senate Armed Services Committee.

"It is a time for all of us to stand with the Ukrainian people in support of their territorial integrity and sovereignty, and their right to have a government that fulfills the aspirations of its people."

The United States has a small team of about 10 airmen stationed in Poland to support military training efforts while Nato has been conducting air patrols over the skies of Estonia, Latvia and Lithuania for 10 years, as those countries do not have viable air forces.