WASHINGTON (AP) — The Pentagon will expand military combat training for Ukrainian forces, using the slower winter months to instruct larger units in more complex battle skills, the Defense Department and U.S. officials said Thursday.

The U.S. has already trained about 3,100 Ukrainian troops on how to use and maintain certain weapons and other equipment, including howitzers, armored vehicles and the High Mobility Artillery Rocket System, known as HIMARS. But senior military leaders for months have discussed expanding that training, stressing the need to improve the ability of Ukraine’s company- and battalion-sized units to move and coordinate attacks across the battlefield.

Air Force Brig. Gen. Pat Ryder told Pentagon reporters Thursday that the U.S. expects to train about 500 Ukrainian troops each month and will begin “in the January timeframe.” Ryder, the Pentagon’s press secretary, added that it is not likely to require additional U.S. forces to conduct the training.

According to U.S. officials, the training will take place at the Grafenwoehr training area in Germany. And the aim is to use the winter months to hone the skills of the Ukrainian forces so they will be better prepared to counter any spike in Russian attacks or efforts to expand Russia’s territorial gains.

The officials, who spoke on condition of anonymity to provide details not publicly announced, said the Pentagon views the expansion as a logical next step for the Ukrainian troops. They said it would mirror, to a limited degree, the types of training that U.S. forces get at Defense Department training centers, such as those in California and Louisiana.

Ryder said it would include classroom instruction and field work that would begin with small squads and gradually grow to involve larger units. It would culminate with a more complex combat exercise bringing an entire battalion together. The training could last as long as a month.

Until now, the U.S. focus has been on providing Ukrainian forces with “immediate battlefield needs” as they defend their country, including specialized equipment training, he said.

“Now as we continue to see Ukraine make progress in terms of pushing Russia back,” said Ryder, “the idea here is to be able to give them this advanced level of collective training that enables them to conduct effective combined arms operations and maneuver on the battlefield.”

He added that the U.S. was doing some of this type of training prior to the Russian invasion in February. But once the war began, U.S. National Guard and special operations forces that were doing training inside Ukraine all left the country. This new effort with larger units would be a continuation of what had been going on before the invasion.

A wide range of Ukrainian troop training is being done in a number of locations across Europe, by the U.S. the British and other allies. It has, for the most part, focused on weapons systems, logistics and other Western equipment.

The expanded U.S. effort will be done by U.S. Army Europe Africa’s 7th Army Training Command. It comes on the heels of the Pentagon’s announcement early last month that it was establishing a security assistance headquarters in Germany that will oversee all weapons transfers and military training for Ukraine.

The new command post, called the Security Assistance Group Ukraine, signals a more permanent, long-term program to continue to aid Kyiv in its fight against Russia.