Washington - Russia has in place about 70% of the combat power it believes it would need for a full-scale invasion of Ukraine. The ground is expected to freeze and harden from mid-February, enabling Moscow to bring in more heavy equipment, the unnamed US officials said on Saturday.
The US officials did not provide evidence for their assessment.
They said the information was based on intelligence but that they were unable to give details due to its sensitivity, US media report.
In the last two weeks, the number of battalion tactical groups in the border region has risen to 83 from 60 as of Friday and 14 more are in transit, the officials told Reuters on condition of anonymity due to the sensitivity of the information.
The growing number and capability of Russian forces close to Ukraine could suggest the window for diplomacy is shutting.
As Russia masses more than 100,000 troops near the border, it has said it is not planning an invasion but could take unspecified military action if its security demands are not met. Those include a promise that NATO will never admit Ukraine, a demand Washington and NATO have said is unacceptable.
The officials also said they did not know if Russian President Vladimir Putin had decided to take such a step, adding that a diplomatic solution was still possible.
If Russia were to invade the capital of Kyiv, it could fall within a couple of days, the U.S. officials said.
A full-scale invasion would cause major casualties, one of the officials said.
Ukraine could suffer 5,000 to 25,000 troop casualties, while Russia's troop casualties could be between 3,000 and 10,000, and civilian casualties could range from 25,000 to 50,000, according to U.S. estimates, the official said.
A full invasion would also prompt the flight of millions of refugees and internally displaced persons in Europe, Washington believes.
Rivalry between Russia and the US, which still possess the world's biggest nuclear arsenals, dates back to the Cold War. Ukraine was then a crucial part of the communist Soviet Union.
-Reuters, BBC