Paweł Soloch made the remark in the US capital on Thursday, Polish state news agency PAP reported.
He added that the war in Ukraine "is entering a key phase and there is a need for quick decisions on supplying Kyiv with weapons.”
'Full support for further assistance'
Soloch, who is a senior aide to Polish President Andrzej Duda, arrived in the US on Wednesday for two days of talks on the latest developments in Ukraine and the West's support for the embattled country, officials told reporters.
On Thursday, the Polish national security official met with US Senate Armed Forces Committee Chairman Jack Reed and Senate Foreign Relations Committee ranking member James E. Risch.
The talks focused on the war in Ukraine and the need to provide Poland’s southeastern neighbour with long-term support, reporters were told.
Soloch, Reed and Risch also discussed the security of Poland as a leading provider of humanitarian and military assistance to Ukraine, the PAP news agency reported.
Reed and Risch “declared their full support for further assistance to Poland and Ukraine,” the Polish president's National Security Bureau (BBN) said.
'Support for countries that supply weapons to Ukraine'
Earlier on Thursday, Soloch was hosted by his US counterpart Jake Sullivan.
The Polish and US national security advisers spoke about Russia's war against Ukraine and Western military assistance to Kyiv, according to officials.
The BBN tweeted that Soloch and Sullivan also discussed "support for countries that supply weapons to Ukraine."
They additionally talked about the decisions of NATO's Madrid summit and Polish-American military cooperation, according to the tweet.
Ukraine war 'entering a key phase’
After Thursday’s talks, Soloch told the PAP news agency that “the war in Ukraine is entering a key phase.”
He said: “The war is still undecided and the next month or so may prove to be game-changing - so there is a need to make quick decisions" on further weapons supplies to Ukraine.
“In this connection, we fleshed out the details of what Polish President Andrzej Duda and US President Joe Biden had discussed earlier,” Soloch said, adding that Duda and Biden explored the issue during informal talks in Brussels earlier this year.
Soloch told reporters: “Officials in Washington are deeply determined to bring about outcomes, including military outcomes, that are favourable to Ukraine.”
His trip to the United States included talks at the Pentagon, the Department of State and the Senate, in addition to meetings with experts from institutions such as the Atlantic Council, the Institute for the Study of War (ISW) and the Heritage Foundation, the PAP news agency reported.
Friday is day 163 of the Russian invasion of Ukraine.
Source: PAP, bbn.gov.pl