President Joe Biden attends a meeting in the Cabinet Room the White House in Washington on Wednesday. AP

President Joe Biden is set to announce plans to send additional military aid to help Ukraine fight back against the Russian invasion, the US official said.

Biden will deliver an update on the Russian invasion of Ukraine on Thursday as he works to complete a new arms package for its military.

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The official, who was not authorized to comment publicly and spoke on the condition of anonymity, said Biden will deliver a Thursday morning address at the White House detailing his plans to build on the roughly $2.6 billion in military assistance the administration has already approved for Ukraine.

A burnt-out bus is seen in front of a residential building damaged during the Ukraine-Russia conflict in Mariupol. Reuters

Biden is to address Americans from the White House Roosevelt Room at 9:45am (1345 GMT) and a source familiar with the planning said he is "expected to provide an update on our efforts to support Ukraine and the assistance we are providing.”

The new arms package was likely to be roughly the same size as an $800 million one announced last week but details were still being worked out, another U.S. official told Reuters earlier.

The new package is expected to be similar in size to the $800 million package Biden announced last week. It includes much needed heavy artillery and ammunition for Ukrainian forces in the escalating battle for the Donbas region of eastern Ukraine.

Earlier this week, Canadian Prime Minister Justin Trudeau also said his country will send heavy artillery to Ukraine. And Dutch Prime Minister Mark Rutte told Ukrainian President Volodymyr Zelensky that the Netherlands will send more heavy weapons, including armored vehicles.

A senior US defence official on Wednesday said training of Ukrainian personnel on American 155mm howitzers has begun in a European country outside Ukraine.