With violence raging in Kiev, Defense Secretary Chuck Hagel has trying to reach his Ukrainian counterpart on the phone to urge restraint against civilian protesters - but no one is picking up, U.S. officials said today.

Indications are that the Ukrainian government's violent crackdown against protesters in Kiev have involved Interior Ministry forces and not military troops, officials said.

Hagel has tried to personally convey to Ukrainian Defense Minister Pavel Lebedev the message that the Ukrainian military should refrain from intervening against civilian protesters, Pentagon Press Secretary Rear Admiral John Kirby said today at a Pentagon news conference.

But "so far the Ministry of Defense has been unresponsive to our requests," Kirby said. "We've been trying now for the past several days as the violence escalated to reach the Ministry of Defense."

He described the ministry's lack of a responsiveness as "pretty unusual."

Kirby said Hagel is "deeply troubled" by the violence in Ukraine and "shares the outrage of so many over images of the Ukrainian Ministry of Interior forces firing automatic weapons at their own people."

Hagel urges the Ukrainian armed forces to continue to refrain from participating in the conflict, Kirby said, "a conflict that can and should be resolved politically."

Hagel routinely reaches out to counterparts, especially to urge military leaders not to intervene in significant political crises. Over the past year he has spoken dozens of times with Egyptian Field Marshal al Sisi to urge that the Egyptian military continue to adhere to political institutions in the wake of President Morsi's removal from power, officials said.

Reports indicate the Ukrainian military is protecting military bases and storage facilities and is not involved in the violence against protesters, Kirby said. "We certainly hope that remains the case," he said.

Hagel last spoke with Lebedev in mid-December as protests began against President Viktor Yanukovich's decision to forego a trade deal with the European Union in favor of one with Russia.

Since the protests began the Pentagon has had "a consistent concern" that the Ukrainian military could be used to end the protests, Kirby said.

Hagel is not the only senior defense leader unsuccessful in trying to contact the Ukrainian military, though those efforts may have been complicated by President Yanukovich's dismissal of Ukraine's top military officer.

NATO Supreme Commander Gen. Phillip Breedlove took to social media on Wednesday as a way of urging the Ukrainian military to not get involved in the violence.

Breedlove tweeted "I am calling upon the new military leadership in Ukraine to open a dialog(ue) with us to bring this situation to a peaceful resolution."

In another tweet he said, "As NATO's military commander I ask that responsible leaders avoid the use of military force against the people of Ukraine."

(T.J. Kirkpatrick/Getty Images)