The United States will bolster military cooperation with Poland and Baltic states to show solidarity with its allies after Russia's intervention in Ukraine, Pentagon chief Chuck Hagel said Wednesday.

The mostly symbolic steps to expand aviation training in Poland and step up the US role in NATO's air patrols over Baltic countries were clearly designed to reassure alliance partners in Central and Eastern Europe following alarm at Russia's actions in the Crimean peninsula.

"This morning the Defense Department is pursuing measures to support our allies," including increased training in Poland and more US aircraft for NATO's air policing mission over Baltic states, Hagel told lawmakers.

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

"This is a time for wise, steady, and firm leadership," Hagel told the Senate Armed Services Committee, describing it as "time for all of us to stand with Ukrainian people in support of their territorial integrity."

At the same hearing, General Martin Dempsey, the US military's top-ranking officer, said he had spoken to his Russian counterpart, General Valery Gerasimov earlier Wednesday, urging "restraint" in the days ahead "to preserve room for a diplomatic solution."

- More aircraft for Baltic patrols -

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.

The responsibility for the air patrols rotates every four months and the United States recently took over from Belgium in January.

There are four US F-15 fighter jets currently flying the air patrols and the Pentagon will send six additional F-15s and one KC-135 aerial refueling tanker to the mission, said a defense official, who spoke on condition of anonymity.

Officials had earlier incorrectly stated that F-16s were carrying out the "air policing" operation.

In Poland, US aviation training involves F-16 fighters and C-130 transport planes and the official said more aircraft may be added to the effort.

The United States already has suspended all military cooperation with Russia in protest over events in Ukraine, calling off planned exercises, training and exchanges.

Hagel dismissed Russia's assertion that it had not sent troops into Crimea and that forces surrounding air bases and other sites were local "self-defense" militias.

"It's pretty clear that they're Russian troops," he said.

Dempsey, chairman of the US Joint Chiefs of Staff, said he had raised the issue with his counterparts, who told him the forces were "well-trained" militia.

"I did suggest that a soldier looks like a soldier, looks like a soldier, and that that distinction had been lost on the international community," he said.

Dempsey added that "these are soldiers who have been taken out of their traditional uniforms, repurposed for placement in the Crimea as a militia force."

The general said he had also spoken this week to military chiefs in the Baltics and in Central and Eastern Europe.

"Understandably, they are concerned. They seek our assurance for their security," he said.

"During our conversations we committed to developing options to provide those assurances and to deter further Russian aggression," the four-star general said.

NATO held rare emergency meetings this week after Poland requested "article 4" consultations in light of the crisis in Ukraine, where pro-Russian forces have taken de facto control over the Crimean peninsula.

Under article 4 of the alliance treaty, any NATO member can request consultations when they believe their territorial integrity, political independence or security are threatened.