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

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.

Germany plans to provide Ukraine with a Patriot air defense battery, the White House confirmed Thursday.

The United States agreed last month to send the first Patriot missile defense system to Ukraine to protect the country against Russia’s ongoing missile and drone attacks targeting its critical infrastructure.

The development came as President Joe Biden spoke by phone Thursday with German Chancellor Olaf Scholtz about the ongoing war.

The White House also said it would send Bradley infantry fighting vehicles to Ukraine. Germany agreed to send Marder infantry fighting vehicles, according to the White House.

"They (Germany) reiterated their support for Ukraine’s sovereignty and independence," the White House said in a statement. "They reaffirmed their unwavering solidarity with Ukraine and the Ukrainian people in the face of Russia’s aggression."

-ABC News' Matt Seyler and Ben Gittleson