Russian jets probe Ukraine airspace again as tensions rise

US defense officials said Friday that Russian fighter jets flew into Ukrainian airspace a handful of times over the last 24 hours, in what one called a continued provocation of the heightened tensions in the region.

The officials said it's not clear what the intent was, but the aircraft could have been testing Ukrainian radar or making a show of force.

Col. Steve Warren, a Pentagon spokesman, confirmed the flights, adding that the U.S. is calling on the Russians "to take immediate steps to de-escalate the situation."

On Saturday, Ukrainian Prime Minister Arseny Yatseniuk told reporters in Rome that "Russian military aircraft today at night crossed and violated Ukrainian airspace seven times. The only reason is to provoke Ukraine ... and to accuse Ukraine of waging war against Russia."

Russia denied the reports. “Russia’s means of objective airspace situation control did not record any violations of air boundaries of the states adjacent to Russia, including those of Ukraine,” the Russian Defense Ministry said in a statement Saturday.

The flights come as Russia increases military exercises along the Ukraine border, including moving a broad array of fixed wing and rotary aircraft, infantry and armored troops. The exercises inflame worries about a potential Russian military incursion into Ukraine.

At the United Nations Friday, Ukraine's deputy foreign minister, Danylo Lubkivsky said he feared an imminent Russian invasion.

"We have the information we are in danger," Lubkivsky told reporters, saying Russian military maneuvers involving air and ground forces along the Ukraine border were a "very dangerous development."

"We are going to protect our motherland against any invasion," Lubkivsky said. "We call on the Russians to stop this madness."

The West has threatened additional sanctions against Russia over its annexation of Ukraine's Crimean region in March and the ongoing escalation of military operations along the border.

On Friday, the US and other nations in the Group of Seven agreed to "move swiftly" to impose additional economic sanctions on Russia in response to its actions in Ukraine. In a joint statement released Friday night by the White House, the G-7 nations said they will act urgently to intensify "targeted sanctions." The statement said the G-7 will also continue to prepare broader sanctions on key Russian economic sectors if Moscow takes more aggressive action.

The White House said U.S. sanctions could be levied as early as Monday.

On Friday, the ratings agency Standard & Poor's cut Russia's credit grade for the first time in five years.

Army Gen. Martin Dempsey, the chairman of the Joint Chiefs of Staff, spoke with his Russian counterpart, Gen. Valery Gerasimov, on Thursday and to express "grave concern" over Russia's aggressive military behavior, the Pentagon said in a statement. "The two military leaders agreed on the need to reduce tension, avoid miscalculation and keep an open line of communication," according to the statement.

Warren said U.S. officials have let Russian defense ministry officials know that US Defense Secretary Chuck Hagel would like to speak to his counterpart, Russia Defense Minister Sergei Shoigu. There has been no response yet, Warren said.

This is the second set of military exercises conducted by the Russians along the border region. The latest exercises were quickly denounced by Hagel, who called them "dangerously destabilizing" and "very provocative." If such activities escalate, they will make it more difficult to find a diplomatic solution to the situation in Ukraine, Hagel said, speaking in Mexico City.