“The strength of the United States Armed Forces remains unquestioned – just ask Iran,” Kelly added, referring to US strikes at three Iranian nuclear sites last month.
The decision comes shortly after US President Donald Trump met with his Ukrainian counterpart Volodymyr Zelensky at the Nato summit in the Netherlands last week.
On that occasion, Trump said US officials “are going to see if we can make some of them available” when asked by the BBC, external about providing extra Patriot anti-missile systems to Ukraine.
Referring to his conversation with Zelensky, Trump said: “We had a little rough sometimes, but he couldn’t have been nicer.”
The two had a heated confrontation in the Oval Office in March this year. Afterwards, Trump said he was pausing military aid to Ukraine that had been earmarked by the previous Biden administration. Intelligence sharing with Ukraine was also suspended.
But both pauses were subsequently lifted.
In late April, the US and Ukraine signed a deal that would give the US access to Ukraine’s mineral reserves in exchange for military assistance.
Separately, French President Emmanuel Macron spoke with his Russian counterpart Vladimir Putin on Tuesday – the first time in over two-and-a-half years.
They spoke on the phone for more than two hours, Macron’s office said, adding that the French president urged a ceasefire in Ukraine.
Putin hit back by blaming the West for the conflict. A Kremlin statement said Putin reminded Macron that Western countries had “for many years ignored Russia’s security interests” and “created an anti-Russian bridgehead in Ukraine”.
The US military aid suspension comes as Russia stepped up its war against Ukraine.
Over the weekend, Russia launched one of its largest aerial attacks on Ukraine since the start of the war, using more than 500 different types of weapons, including drones, ballistic and cruise missiles.
On Tuesday, three people were killed in a Ukrainian attack on a Russian factory in Izhevsk, more than 1,000km (620 miles) from the border with Ukraine.
Moscow currently controls about 20% of Ukrainian territory, including the Crimea peninsula annexed in 2014.