US supports Ukraine against 'reckless' Russian moves - Blinken

US Secretary of State Antony Blinken said on Thursday Washington could increase security assistance for Ukraine after what he called Russia's "reckless and aggressive" actions in massing troops near the Ukrainian border.

During a visit to Kyiv, Blinken said Russia had left behind significant quantities of soldiers and equipment despite announcing a withdrawal of its forces from the area after a standoff that alarmed the West.

Blinken also said President Joe Biden was keen to visit Ukraine and meet President Volodymyr Zelenskiy, but gave no details on that, or on Washington's view of Ukraine's aspirations to join the NATO military alliance.

"I can tell you, Mr President, that we stand strongly with you, partners do as well. I heard the same thing when I was at NATO a couple of weeks ago and we look to Russia to cease reckless and aggressive actions", Blinken said, speaking alongside Zelenskiy.

He said Washington was "actively looking at strengthening even further our security cooperation and our security assistance," but gave no details.

In Washington, White House spokeswoman Karine Jean-Pierre, asked about Ukraine said the administration was committed to keeping the door open for countries to join "when they are ready and able to meet the commitments and obligations of membership and can contribute to security in the Euro-Atlantic area."

Zelenskiy said Russia had withdrawn only about 3,500 of the tens of thousands of troops deployed to the Crimean Peninsula, which it annexed from Ukraine in 2014. "There may be a threat. Nobody wants these surprises," he said.

Blinken also urged Ukraine to stick to a path of fighting corruption and the influence of oligarchs. The State Department expressed concern about the firing of a reformist energy official last week.

Biden had pledged "unwavering support" to Zelenskiy in April as Kyiv and Moscow traded blame for clashes between Ukraine's army and pro-Russian rebels in the eastern Donbass region, as Russia was deploying more troops to the border area. 

Moscow announced a withdrawal of its forces on April 22, helping to smooth preparations for a summit between Biden and Russian President Vladimir Putin that Biden would like to take place next month. 

The standoff prompted Ukraine to urge the United States and Europe to help accelerate its entry into NATO. 

Washington has been Kyiv's most powerful backer since Russia annexed Crimea and the conflict in eastern Ukraine began. Kyiv says the fighting has killed 14,000 people in seven years.

The relationship was tested in 2019 when then-president Donald Trump asked Zelenskiy to investigate Biden and the business activities of his son Hunter in Ukraine, and the Trump administration temporarily froze security aid to Kyiv.

The fallout from those events, which led to Trump's impeachment, continued last week as federal agents raided the apartment and office of Trump's former personal lawyer, Rudy Giuliani, in relation to his activities in Ukraine. 

Zelenskiy, asked about Giuliani, said: "I don't want to waste your time on the past, let's talk about the future."

Kyiv would like Washington to sell it more weaponry. Foreign Minister Dmytro Kuleba told Reuters last month that this included equipment to counter Russia's capacity to jam Ukrainian communications. 

In a CNN interview, Kuleba said Ukraine was also asking for air defense systems and anti-sniper technology.

After meeting Blinken on Thursday, Kuleba said he had been assured that nothing would be decided between Putin and Biden without taking Ukraine's interests into account.