Counting Russian troops is an imprecise science.

The United States now believes that Russia has as many as 190,000 troops in or near Ukraine, nearly twice as many as there were in January, according to an assessment made public on Friday by Michael Carpenter, the U.S. ambassador to the Organization for Security and Cooperation in Europe.

That was a significantly higher number than the 150,000 troops President Biden referred to earlier this week, and the 100,000 in January.

But American officials said the new number includes some forces that were not previously counted — most notably Russian forces in Crimea, as well as separatist forces led by Russian military officers in the Donbas region, a portion of eastern Ukraine they have controlled since 2014. The officials did not provide a breakdown of these forces.

The new number also includes some additional forces that have moved into Belarus, according to American officials briefed on the intelligence. And the combat forces have increased, according to a defense official. There are now between 120 and 125 battalion tactical groups, up from 83 earlier in February.

Counting Russian forces is an imprecise science. The size of Russian battalions can vary, depending on their role. And while Russia has taken fewer pains to hide the movement of troops in recent weeks, moving units during the day rather than at night, the United States has not detected all of Russia’s combat preparations, officials said.

Russia has also, according to outside analysts, blocked some means of monitoring Russian rail traffic, which had been used to count forces flowing to and from the Ukrainian border.

A U.S. defense official said that as many as 75,000 of the Russian forces outside of Ukraine were in combat formations, ready to mount a full-scale invasion in days.

U.S. and allied officials have been divided on whether Russia intends an invasion aimed at occupying a wide swathe of the country, or if it wants simply to solidify its control in the Donbas region. But the defense official said that within the Russian forces outside Ukraine’s borders are reservist units, the kinds of forces that would be tasked not with taking new territory but with conducting occupation operations. And even as Russia has made a show of pulling back some forces, it has pushed other forces closer to the border.

Thomas Bullock, a senior open-source intelligence analyst with Jane’s, said Russia had moved air defense systems, long-range artillery and army units to sites about 18 miles from Ukraine’s borders in recent days, particularly in the area where the borders of Ukraine, Belarus and Russia converge.

“It’s very difficult to hide at this stage because the world is watching and they are moving a lot of equipment in,” Mr. Bullock said.