"Russia could invade Ukraine in the next few weeks and there's low to medium chances of this happening" said the US General in Europe as tensions increase multi-fold between the two countries.

Russia on Friday banned top officials from U.S. President Joe Biden's administration from entering the country as it announced a wave of tit-for-tat sanctions and expulsions of diplomat. They announced that top U.S. officials including Attorney General Merrick Garland, Biden's chief Domestic Policy Advisor Susan Rice, and FBI chief Christopher Wray would be banned from entering Russia. 

On Thursday, Washington had announced sanctions and the expulsion of 10 Russian diplomats in retaliation for what it says is interference by the Kremlin in U.S. elections, a massive cyber attack and other hostile activity.

The Pentagon has declined to detail its assessment on the size and composition of those troops, referring reporters to Moscow. However, the White House disclosed that Russia has more troops on Ukraine's eastern border than at any time since 2014, when it annexed Crimea and backed separatist territory seizures.

Ukraine and Russia have traded blame over a spike in violence in the conflict in eastern Ukraine, where Ukrainian troops have battled Russian-backed forces in a conflict that Kyiv says has killed 14,000 people since 2014.

In recent weeks, Russia's massing of troops on Ukraine's northern and eastern borders, and on the Crimean peninsula it annexed seven years ago, have contributed to the sharp escalation in tensions.

U.S. forces in Europe have raised their alert status in response, while NATO has issued warnings to Moscow.