Ukraine crisis: Obama praises 'excellent' Poroshenko
President Barack Obama has given his support to Petro Poroshenko, describing himself as a "strong friend" to Ukraine's leader.
Mr Obama condemned what he called Russian aggression in eastern Ukraine.
He called for the withdrawal of Russian troops from Ukrainian territory and the closure of the border to arms.
But he stopped short of agreeing to Mr Poroshenko's request for US military assistance to his country to counter pro-Russian eastern separatists.
"Congratulations on the excellent work that you've done," said Mr Obama during a bilateral meeting in the Oval Office.
"You have a strong friend not only in me personally, but I think, as you saw in Congress today, you have strong bipartisan support here in the United States."
Mr Obama has said military support will only include non-lethal weapons.
Mr Poroshenko told the joint session of Congress in Washington that Ukrainian government forces needed more equipment - both lethal and non-lethal.
"Blankets, night-vision goggles are important, but one cannot win the war with blankets."
His impassioned plea for US support brought applause and several standing ovations.
More than 3,000 people have died in fighting between Ukrainian government forces and pro-Russian rebels in the eastern Donetsk and Luhansk regions since April.
Both the US and the European Union have recently imposed a new round of sanctions against Russia over its role in the Ukraine crisis.
In his address to Congress, Mr Poroshenko accused Russia of being motivated by an "imperial mindset" and "nostalgia for the Soviet Union" in its annexation of Crimea in March and by supporting the separatists in eastern Ukraine.
And he called on the US to give Ukraine a "special security and defence status which reflects the highest level of interaction with non-Nato allies" in the face of Russian aggression, which he described as a threat to "global security everywhere".
On Tuesday, Ukraine's MPs approved a bill granting self rule to parts of the Donetsk and Luhansk regions - a move described as "capitulation" by some lawmakers.
Analysis: Jon Sopel, BBC North America editor
Ukraine's President Petro Poroshenko was cheered as he was introduced by House Speaker John Boehner.
The president's speech was punctuated by repeated applause and standing ovations. US lawmakers wanted to show him that his fight was their fight.
But Mr Poroshenko, no doubt gratified by the reception, had an agenda wider than just bathing in the love of Congress. He wants action: enhanced military status, weaponry, tougher sanctions against Russia.
That might prove more difficult to obtain than the backslaps and warm handshakes.