Russia-Ukraine updates: Putin suspends key US-Russia nuclear treaty

As many as 100 Ukrainians troops will soon begin training on the Patriot air defense system at Fort Sill, Oklahoma, two U.S. officials told ABC News Tuesday.

Fort Sill is the main artillery school for the U.S. Army and where months-long training on Patriot systems already takes place.

Brig. Gen. Pat Ryder, a Pentagon spokesperson, said the Ukrainians could begin training on the Patriot system as soon as next week.

"The training will prepare approximately 90 to 100 Ukrainian soldiers to operate, maintain and sustain the defensive system over a training course expected to last several months," Ryder said.

Once deployed, the Patriot batteries will fortify Ukraine's air defense capabilities and provide an additional way for the "Ukrainian people to defend themselves against Russia's ongoing aerial assaults," Ryder said.

Ryder would not give a precise time frame, but said that once the training is completed, the system will be sent to Ukraine to be put to use.

President Joe Biden announced last month that the United States will provide Ukraine with a Patriot missile defense system. The German government also agreed this month to supply Ukraine with a second Patriot missile battery.

-ABC News' Matt Seyler

Russian troops were on the verge Tuesday of capturing a salt mining town in eastern Ukraine in an apparent attempt to cut off the enemy's supply routes, according to British intelligence officials.

The Russian forces, along with mercenaries from the Wagner private military company, were likely in control of the city of Soledar, which is about six miles north of Bakhmut in the Donbas region, where heavy fighting has been reported in recent days, the British officials said.

The attack on Soledar is an apparent attempt to bypass Bakhmut from the north and disrupt Ukrainian supply routes, the British intelligence officials said. Part of the fighting is being waged near the entrances to the 124 miles of abandoned salt mine tunnels that run under the area.

Despite the increased pressure on Bakhmut, Russia is unlikely to be able to encircle the city in the near future because Ukrainian forces have created a stable line of defense and control supply routes in the area, the British officials said.

The Ukrainian Army said Russian troops carried out 86 artillery strikes on Soledar in a 24-hour period, and Ukrainian President Volodymyr Zelenskyy has described the fighting there as "very difficult."

The White House announced Friday that the U.S. would provide $3 billion more in military assistance to Ukraine, including Bradley Fighting Vehicles for the first time.

“Today, the United States will demonstrate our continued, enduring commitment to Ukraine's ability to defend itself with the announcement of over $3 billion in new military assistance to Ukraine, including a $2.8 billion drawdown for Ukraine, the largest yet,” White House press secretary Karine Jean-Pierre said.

Moreover, the U.S. will provide $682 million "for regional partners and allies on NATO's eastern flank to incentivize and backfill donations of military equipment," said Jean-Pierre.

-ABC News' Ben Gittleson

Russian President Vladimir Putin declared a Christmas "truce" for the next 36 hours with a temporary cease-fire set to end at midnight on Jan. 7.

Air raid sirens sounded across several southern and eastern regions of Ukraine a few hours before the cease-fire started.

However, Ukrainian President Volodymyr Zelenskyy last night called the truce a "cover" to stop Ukraine from advancing in the east.

The Russian Orthodox Church celebrates Christmas Day on Jan. 7, but the brief unilateral Russian cease-fire called by Putin is not expected to last beyond the announced period.

The temporary cease-fire could put Ukraine in a difficult position. If it seeks to stop Russia from regrouping its forces during the cease-fire, it could be accused of violating a truce it never agreed to in the first place and be portrayed as aggressive. However, if Ukraine stops fighting for the 36-hour period, it will likely face a more dangerous position when the cease-fire ends.