Kamala Harris, the US vice-president, has indirectly denounced the Trump campaign’s policy on ending Russia’s war against Ukraine as “proposals of surrender” as the Ukrainian leader Volodymyr Zelenskyy visited Washington to present his own “victory plan”.

Addressing Zelenskyy at the White House, Harris said that “some in my country” would pressure Ukraine to accept a peace deal in which it surrendered its sovereign territory and neutrality in order to make peace with Vladimir Putin.

“These proposals are the same as those of Putin, and let us be clear, they are not proposals for peace,” she said. “Instead, they are proposals for surrender, which is dangerous and unacceptable.”

While she did not mention Donald Trump or JD Vance by name, those terms for peace closely resemble ones laid out by the Republican vice-presidential nominee in a controversial interview earlier this month.

Zelenskyy had publicly denounced Vance as “too radical” after those remarks, sparking a conflict with Trump allies that has culminated with accusations of election interference and Republican calls for Ukraine to fire its ambassador to Washington.

In an apparent U-turn late on Thursday, the Republican candidate told reporters that he would meet Zelenskyy at Trump Tower in New York on Friday morning.

Harris’s remarks came after Zelenskyy met Joe Biden at the White House for the formal presentation of Zelenskyy’s high-stakes proposal, which he has said can end the war with Russia with additional American aid.

The White House issued a short statement after the meeting, saying that the “two leaders discussed the diplomatic, economic, and military aspects of President Zelenskyy’s plan and tasked their teams to engage in intensive consultations regarding next steps”.

“President Biden is determined to provide Ukraine with the support it needs to win,” the statement said.

Zelenskyy has kept the details of the plan secret, but US officials have said it includes additional American aid to prevent a Ukrainian rout on the battlefield and “provide the [Ukrainian] people with the assurance that their future is part of the west”.

Zelenskyy faces an uphill battle in securing support for the plan, because of caution among senior officials in the Biden administration about providing Russia with a pretext to escalate the conflict further, and the looming November presidential elections that could lead to a re-election of Donald Trump.

Ahead of the meeting, Biden announced more than $8bn in military assistance to Kyiv, calling it a “surge in security assistance for Ukraine and a series of additional actions to help Ukraine win this war”.

The aid includes the provision of a medium-range “glide bomb” munition fired from fighter jets that would allow Ukrainian forces to strike Russian troops and supply lines at safer distances.

The allocation included $5.5bn from the Ukraine security assistance initiative fund by the end of the year, as well as an additional $2.4bn in security assistance via the Department of Defense.

The package includes additional Patriot air defense battery and missiles, unmanned aerial systems, and measures to strengthen Ukraine’s defense industrial base, Biden said. The US will also expand training for additional F-16 fighter pilots, with an extra 18 pilots to be trained next year.

But Biden was not expected to grant a key Ukrainian request that has been supported by the UK – permission to use arms such as long-range Atacms ballistic missiles to strike targets deeper inside Russia – due to fears of escalating the conflict with Russia.

“There is no announcement that I would expect [on that],” the White House press secretary, Karine Jean-Pierre, told reporters before the meeting.

Zelenskyy said in a social media post: “We will use this assistance in the most effective and transparent way possible to achieve our main common goal: a victorious Ukraine, a just and lasting peace, and transatlantic security.”

Biden also announced that he would convene a high-level meeting of the Ukraine defense contact group to coordinate aid to Ukraine among more than 50 allies as he enters the lame-duck period of his final three months in office.

US media have reported that the Biden administration and European allies have been skeptical of Zelenskyy’s plan to achieve victory, which is understood to secure maximal support from the west ahead of potential negotiations with Russia.

“I’m unimpressed. There’s not much new there,” a senior official told the Wall Street Journal.

Zelenskyy had said the plan included decisions that can be taken “solely” by the United States and “is based on decisions that should take place from October through December” – meaning the end of Biden’s term in office.

The meeting comes amid rising tensions between Zelenskyy and the Republican presidential candidate, who has attacked the Ukrainian leader for “making little nasty aspersions toward your favourite president: me”.

Zelenskyy, in an interview with the New Yorker published this week, said he believed Trump “doesn’t really know how to stop the war” and that his running mate, Vance, was “too radical” for describing a vision for peace that included Ukraine ceding territories currently occupied by Russia.

Before the meetings, Zelenskyy met members of Congress from both parties on Capitol Hill.

On Wednesday, the House speaker, Mike Johnson, a Republican, accused Zelenskyy of election interference and demanded he fire his ambassador to Washington over a visit to an ammunitions factory in the battleground state of Pennsylvania. Johnson claimed the Ukrainian ambassador had failed to invite any Republicans to the event and called it a “partisan campaign event designed to help Democrats”.

Zelenskyy sought to reduce tensions on Thursday as he thanked the US for the new arms package and praised political leaders’ “strong bipartisan support” in “Ukraine’s just cause of defeating Russian aggression”.

“I am grateful to Joe Biden, [the] US Congress and both parties, Republicans and Democrats, as well as the entire American people for today’s announcement of major US defence assistance for Ukraine, totalling $7.9bn and sanctions against Russia,” Zelenskyy wrote.

Nonetheless, US and European officials have noted with varying levels of alarm the potential for a Trump administration to sharply reduce US aid to Ukraine in order to force Zelenskyy to accept terms for a ceasefire.

Asked if the Democrats wanted to “Trump-proof” aid to Ukraine before a potential Trump presidency, a senior state department official said, “I don’t ever talk in those terms” but that the primary goal was to make sure Ukraine “has all the equipment it needs to keep fighting and manpower and other things”.

“At the end of the year, regardless of who wins our election in December, as at the end of this fighting season, Zelenskyy and Putin need to look at the battlefield and say, here’s what we think next year will look like,” the official said.

“And the primary factor there is, do I think the other side has all the equipment it needs to keep fighting and manpower and other things?”