THE HAGUE - As President Obama convened an emergency meeting of the G-7 leaders today to turn up the heat on Moscow, the Russian military has added to their forces on Ukraine's border.

U.S. officials tell ABC News that Russia has sent an additional 10,000 troops to the Ukraine border in the past week, bringing the Russian force there to almost 30,000.

While Russia claims the troops movements are part of military exercises, White House Deputy National Security Adviser Ben Rhodes told reporters, "There's every reason to be skeptical of Russian assertions."

Seeking to mobilize the international community to further isolate Russia, Obama met with the G-7 leaders to strategize a response to Russia's takeover of Ukraine's Crimean peninsula.

"There have to be consequences. And if Russia continues to escalate the situation, we need to be prepared to impose a greater cost," the president reiterated in an interview with a Dutch newspaper.

Today's hastily arranged meeting, on the sidelines of the Nuclear Security Summit, was intended to foreshadow the sanctions Russia will face if it continues down this path, Rhodes said.

The leaders were also expected to discuss Russia's future as a member of the G-8, although Rhodes said the U.S. was not prepared to formally kick Russia out just yet. "The door is open to Russia to deescalate the situation," he said.

The meeting came after top NATO and Ukrainian officials said Sunday they worry that Russia is poised to escalate the conflict.

Appearing on "This Week," Ukrainian Foreign Minister Andrii Deshchytsia said that the chances of war are "still very high" and "growing."

NATO's top military commander, U.S. Air Force General Philip Breedlove, speaking at a conference in Brussels, warned that the Russian force at the eastern Ukrainian border "is very, very sizeable and very, very ready."

Last Thursday Defense Secretary Hagel received assurances from Russian Defense Minister Shoigu that the Russian troops along eastern Ukraine's border region are there only for exercises and won't cross the border into Ukraine.

Breedlove noted those assurances might be suspect given Russia's military push into Crimea occurred after military exercises.

"We saw several snap exercises executed in which large formations of forces were brought to readiness and exercised and then they stood down. And then as we have all seen, a snap exercise with large formations brought into readiness and boom, into Crimea, they went, with a highly prepared force," he said.

Although Ukraine pulled its troops out of Crimea today, the White House insists the peninsula is not lost because the international community rejects the referendum.