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President Joe Biden has said the US will provide Ukraine with more advanced rocket systems and munitions so it can "more precisely strike key targets on the battlefield".
"We have moved quickly to send Ukraine a significant amount of weaponry and ammunition so it can fight on the battlefield and be in the strongest possible position at the negotiating table," Mr Biden said in an opinion piece in The New York Times, published late on Tuesday.
He had said on Monday that the US would not send Ukraine “rocket systems that can strike into Russia".
Any weapons system can shoot into Russia if it is close enough to the border, but US officials said they had reassurances from Ukraine that they would not fire beyond Ukraine's borders.
An aid package expected to be unveiled on Wednesday would send what the US considers to be medium-range rockets that generally can travel about 80 kilometres, US officials said.
“If Russia does not pay a heavy price for its actions, it will send a message to other would-be aggressors that they too can seize territory and subjugate other countries,” Mr Biden wrote.