Russia has gathered about 70% of the military combat power needed for a full-scale invasion of Ukraine, two U.S. officials told Reuters on Saturday.

Despite denying any intention to invade Ukraine, Russia has amassed about 100,000 troops near its border. The move has come as Russia has maintained demands that Ukraine be denied NATO membership.

Russia’s battalion tactical groups have also greatly risen in two weeks. The U.S. officials told Reuters that the groups went from 60 to 83 as of Friday with 14 more in transit.

The officials also were informed that Russia is betting on the primal weather conditions within the next week so that the ground is in “peak freeze” to transport off-road mechanized military units.

"We are in the window,” White House national security adviser Jake Sullivan said Sunday on Fox News. “Any day now, Russia could take military action against Ukraine or it could be a couple of weeks from now, or Russia could choose to take the diplomatic path instead.”

The U.S. has reportedly suspected that Moscow might move forward with a limited incursion, rather than a full-scale invasion. It is also believed that President Vladimir Putin has not made a final decision, but that he is putting a plan in place to be prepared for all scenarios.

The Biden administration has threatened severe economic sanctions on Russia if Ukraine is invaded.

U.S. officials told Reuters that Ukraine’s capital could be invaded and fall in a matter of days. There would also be mass casualties.

It is estimated that Ukraine could suffer 5,000 to 25,000 troop casualties. Russia's troop casualties could be between 3,000 and 10,000. Civilian casualties could range from 25,000 to 50,000.