WASHINGTON — The Pentagon is expanding the training the U.S. military provides to Ukrainian troops, with plans to more than double the number of forces it instructs at a base in Germany, the Defense Department and U.S. officials said Thursday, using the slower winter months to instruct larger units in more complex battle skills.

The expanded training, which officials said President Joe Biden approved this week, would enable U.S. instructors to train a Ukrainian battalion — about 600 to 800 troops — each month, beginning early next year, officials said.

That is a major increase in the overall number of Ukrainians the United States trains outside the country — now averaging about 300 troops a month — as well as a revamping of the training they will receive.

Since the war started in February, the United States has trained a total of 3,100 Ukrainian soldiers, mostly in small groups, on specific weapons like various artillery systems, according to Defense Department statistics.

Meanwhile, Russia’s Foreign Ministry warned Thursday that if the U.S. delivers sophisticated air defense systems to Ukraine, those systems and any crews that accompany them would be a “legitimate target” for the Russian military, a blunt threat that was quickly rejected by Washington.

U.S. officials said Tuesday that Washington was poised to approve sending a Patriot missile battery to Ukraine, finally agreeing to an urgent request from Ukrainian leaders desperate for more robust weapons to shoot down incoming Russian missiles that have crippled much of the country’s vital infrastructure. An official announcement is expected soon.

Operating and maintaining a Patriot battery requires as many as 90 troops, and for months the U.S. has been reluctant to provide the complex system because sending American forces into Ukraine to run the systems is a nonstarter for the Biden administration.

But the U.S. plans for more overall training of Ukrainian forces in Germany could likely include training on the Patriot system.

The Pentagon has trained 610 Ukrainian soldiers in the use of High Mobility Artillery Rocket Systems, or HIMARS, an advanced rocket launcher. Ukrainian troops have used the launchers to devastating effect, hitting targets far behind the lines, including ammunition depots, command posts and bridges.

Russian Foreign Ministry spokeswoman Maria Zakharova said the U.S. had “effectively become a party” to the war by providing Ukraine with weapons and training its troops.

She added that if reports about U.S. intentions to provide Kyiv with Patriot surface-to-air missile system prove true, it would become “another provocative move by the U.S.” and broaden its involvement in the hostilities, “entailing possible consequences.”

“Any weapons systems supplied to Ukraine, including the Patriot, along with the personnel servicing them, have been and will remain legitimate priority targets for the Russian armed forces,” Zakharova declared.

Asked about the Russian warning, Pentagon spokesman Air Force Gen. Pat Ryder responded that the U.S. was “not going to allow comments from Russia to dictate the security assistance that we provide to Ukraine.”

“I find it ironic and very telling that officials from a country that brutally attacked its neighbor — in an illegal and unprovoked invasion, through a campaign that is deliberately targeting and killing innocent civilians and destroying civilian infrastructure — that they would choose to use words like ‘provocative’ to describe defensive systems that are meant to save lives and protect civilians,” Ryder said.

Under the expanded training program, U.S. personnel will instruct larger groups of Ukrainian soldiers in more advanced battlefield tactics, including “collective training,” like coordinating ground infantry troop maneuvers with artillery support.

CNN reported last month that the Biden administration was considering the expanded training.

The new training regimen would take place at a U.S. Army base in Grafenwoehr, Germany, where the Pentagon conducts its own combined arms training. The base is also home to the Joint Multinational Training Group-Ukraine.

Ukrainian officials have been wary of pulling too many troops off the front lines at any given time for specialized weapons training.

But with winter slowing the tempo of fighting in many parts of the combat zone, officials said the coming months would provide a window.

Associated Press contributed.