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

Russia has replaced the military chief in charge in Ukraine, according to the Kremlin.

Army Gen. Valery Gerasimov, chief of the general staff of the Russian armed forces, will replace Sergei Surovikin, who has been commander of Russia's forces in Ukraine for the past three months. Surovikin will become one of Gerasimov's deputies, according to Sergei Shoigu, Russia's minister of defense, who made the new appointments.

The changes come as the progress of the Russian forces in Ukraine continues to stall.

"The increase in the level of leadership of the special operation is linked to the expansion of the scale of the tasks at hand and the need to organize closer interaction between troops," Shoigu said.

Ukrainian officials on Wednesday denied reports that the eastern Ukrainian city of Soledar is on the verge of being captured by Russian forces and claimed the battle for the city is ongoing.

The report contradicts British intelligence officials who on Tuesday said it appeared that Russian troops were close to capturing a salt mining town in an apparent attempt to cut off the enemy's supply routes. The British officials said 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 head of the Wagner group also released a statement on Telegram Tuesday, saying his mercenaries were in control of Soledar.

But Ukrainian officials said Wednesday the city has not fallen into the hands of Russian forces and the Russian mercenary group.

"Russians say that it is under their control; it is not true," said Serhiy Cherevatyi, a spokesperson for the Ukrainian eastern military command.

The Russian 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.

On Tuesday, Ukrainian President Volodymyr Zelenskyy described the fighting in Soledar as "very difficult."

Senior Ukrainian officials said Tuesday that they believe any prospect of Russia launching a new offensive toward Kyiv from Belarus is "not likely at this moment."

The latest statement from Ukrainian officials contrasted with a series of interviews they gave last month in which they suggested Russia could mount an offensive early this year and even try to take Kyiv.

"Our assessment is that the Russians aren't in a position to make an advance on Kyiv from Belarus. And if that were their intention, it wouldn't happen for some time," a senior Ukrainian official said Tuesday.

The Ukrainian officials added that the mere threat of an assault from Belarus means that Ukrainian forces are "fixed" along the Ukraine-Belarus border.

-ABC News' Tom Soufi Burridge

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