Russia-Ukraine updates: 2 US veterans who joined Ukrainian forces missing

The Russian defense ministry claimed it fired on the Ukrainian Apache, a dry-cargo ship, which allegedly changed course and attempted to break through to the Mariupol seaport, the ministry said.

The Ukrainian dry-cargo ship did not respond to Russian border guards' demands to contact them through the international channel and continued heading in the direction of Mariupol port, Russia claimed.

Russia said two border patrol ships fired warning artillery along the vessel's course, but the cargo ship did not change course or slow down.

The cargo ship, over radio communication, transmitted a message, saying, "I am 'Maniac', coming for you," and signal fires were observed on the shore, according to Russia's defense ministry.

The Black Sea Fleet then opened artillery fire on the Apache dry-cargo ship to block the vessel, Russia's defense ministry said.

A direct hit caused a fire in the stern of the ship and it then went adrift. The crew got in touch with border ships with a request to cease fire and said they will comply with the demands of Russian sailors, Russia said.

Russia said no crew members were injured and the fire was extinguished by the ship's crew.

The ship was inspected and then convoyed to the Yeysk port along with its crew, according to Russia.

British Prime Minister Boris Johnson met with Ukrainian President Volodymyr Zelenskyy in Kyiv on Saturday, according to the Ukrainian Embassy in London.

"The Prime Minister of the United Kingdom Boris Johnson is one of the most principled opponents of the Russian invasion, a leader in sanctions pressure on Russia and defence support for Ukraine. Congratulations in Kyiv, my friend!" Zelenskyy said in a post online.

Britain announced it will send 120 armored vehicles and new anti-ship missile systems to support Ukraine, according to the The Associated Press.

"Today I met my friend President @ZelenskyyUa in Kyiv as a show of our unwavering support for the people of Ukraine. We're setting out a new package of financial & military aid which is a testament of our commitment to his country's struggle against Russia’s barbaric campaign," Johnson said.

Ukraine claimed Saturday that its intelligence indicates Russian forces are currently regrouping in eastern Ukraine, then the tankers intend to move toward Kharkiv, Ukraine's Defense Intelligence Chief Kyrylo Budanov said.

Russians are also regrouping in the direction of Izum, in the Kharkiv region, the Ukrainians said.

"They plan to enter Kharkiv in the first place. They will try to conquer the city of Mariupol and only after that they can try to initiate Kiev," Budanov said in an interview on CNN.

To compensate for their significant losses in Ukraine, the Russian army is transferring additional troops to Belgorod (Russia), from where they are relocated to Kharkiv region, the Ukrainians claimed.

Budanov said Ukraine needs serious military support from allies so its soldiers can more effectively resist Russian aggression.

-ABC News' Mike Trew

Ukrainian President Volodymyr Zelenskyy called Friday's deadly missile attack on the Kramatorsk train station in eastern Ukraine "another war crime of Russia."

"All the world's leading powers have already condemned Russia's attack on Kramatorsk," Zelenskyy said during his latest national address Friday. "We expect a firm, global response to this war crime."

The president called for the missile strike, which killed at least 50, to be among the charges in a war crimes tribunal against Russia.

"All the efforts of the world will be aimed to establish every minute: who did what, who gave orders. Where did the rocket come from, who was carrying it, who gave the order and how the strike was coordinated," Zelenskyy said. "Responsibility is inevitable."