US President Joe Biden is in the Ukrainian capital Kyiv on his first visit to the country since Russia’s invasion on 24 February last year.
The White House said Mr Biden would announce more sanctions on Russia and military support for Ukraine including artillery ammunition, anti-armour systems and air surveillance radars.
Ukrainian President Volodymyr Zelenskyy says the pair discussed long-range weapons and described negotiations as “fruitful”.
Mr Biden says Russian President Vladimir Putin thought Ukraine was “weak and the West was divided” and “thought he could outlast us”, adding that he was “dead wrong”.
He added that Washington would provide Kyiv with a new military aid package worth $500 million which would be announced on Tuesday.
In a statement from the White House, the President said he will announce “another delivery of critical equipment, including artillery ammunition” and added that there will be a new Russia sanctions package later this week.
“One year later, Kyiv stands. And Ukraine stands. Democracy stands,” Mr Biden said.
Ukrainian President Zelenskyy described Mr Biden’s visit is an “extremely important sign of support for all Ukrainians” and added that negotiations between the pair were “crucial”.
He goes on to say that he will continue to do everything possible to make sure the democratic world “wins in this historic fight”.
Mr Biden said the package would also provide more ammunition for High Mobility Artillery Rocket Systems in Ukraine’s possession.
The unannounced trip comes after the White House said last week that there were no plans for the president to cross into Ukraine during his visit to Poland this week, to mark the anniversary of Russia’s invasion.
His visit came a day before Russian President Vladimir Putin was due to make a major address, expected to set out Russia’s aims for the second year of the invasion he launched last year.
In December, Mr Zelenskyy visited President Biden at the White House on his first trip out of Ukraine since the war began.