Volodymyr Zelenskiy’s visit to the White House confirmed that Ukraine and the US are “strategic partners” for the first time in history, the Ukrainian leader’s most senior adviser has said in an interview on his return home.

Andriy Yermak, the head of the Ukrainan president’s office, told the Guardian that the trip on Wednesday had cemented Zelenskiy’s bond with the US president, Joe Biden – and with senior US Republicans, despite “dirty” comments made by the Fox News host Tucker Carlson.

The summit and press conference between the two leaders this week demonstrated “how deeply in personal attitude President Biden feels everything which is connected to Ukraine”, Yermak said, and that the US was “a real leader of the free world and democracy”.

Yermak’s emphasis on the personal links forged by the surprise visit, the first time Zelenskiy had been outside Ukraine since the start of the war, comes despite a failure to immediately obtain the US Abrams tanks, F-16 fighter jets and long-range army tactical missile system ATACMS that Ukraine has said it needs to defeat Russia.

But it demonstrates a belief in Kyiv that Ukraine must emphasise the moral dimension of its fight against the invading Russian army and its faith in its relationship with the US to unlock more and more of the military aid it badly needs as the war heads towards its first anniversary in February.

“It’s [the] first time in history that Ukraine and [the] United States are close as strategic partners. There is a very warm, very friendly relationship, [a] personal relationship between [the] two presidents,” said Yermak, who was by Zelenskiy’s side during the trip.

As well as the meeting with Biden, Yermak highlighted meetings Zelenskiy had with US congressional leaders, including those with senior Republicans Mitch McConnell, the senate minority leader, and Kevin McCarthy, the leading candidate to become House speaker next month.

The Ukrainian contrasted that with the attitude of Carlson, who said Zelenskiy looked like “a manager of a strip club” who should have been thrown out of Congress for wearing his trademark khaki fatigues when he addressed the country’s lawmakers.

Carlson was “saying dirty things”, Yermak said, but “he’s not the voice of the Republican party, he’s not the voice of [the] GOP and I can make that conclusion after we met with representatives of [the] GOP in the Congress”.

During the visit, Biden did announce $1.85bn (£1.54bn) in new military assistance to Ukraine, including the delivery of a single Patriot missile defence system, a longstanding request from Kyiv to help it better defend its cities and electricity grid, now prone to repeated blackouts after sustained Russian bombing.

Now back in Kyiv, speaking via a video call, Yermak said he believed this would help unlock other military support. “I hope that we will receive everything which we need and this visit will send a very strong signal for all allies that our United States believes in our victory,” the presidential aide said.

Kyiv has been calling for a mixture of US and European weapons, such as the German-made Leopard tanks and Marder infantry fighting vehicles, as it tries to find a way to break through Russia’s frontlines in the new year.

Yermak declined to say when or where Ukraine might launch its next counterattack, but he predicted 2023 would be a decisive moment in the war. “We will do everything we can to retake our territory. I understand it will be difficult and hard work. Our great, brave nation will continue to fight. I’m sure next year really will be victory year.”

Asked if victory included taking back Crimea, annexed by Russia in 2014, he replied: “Absolutely.” The US administration has not explicitly backed Zelenskiy’s vow to reclaim the peninsula – a mission that most analysts believe would be difficult for Ukraine’s army.

The chief of staff said he did not want to speculate on Vladimir Putin’s trip this week to meet Belarus’s dictator, Alexander Lukashenko, in the capital, Minsk. A recent buildup of Russian troops along the border with Ukraine has fuelled fears Putin may be planning to again attack from the north, in another attempt to seize Kyiv, similar to Russia’s doomed advance in February.

“We have danger along the whole border,” Yermak said, adding: “I’m not keen to know what’s going on inside Putin’s head.” He said Kyiv had received intelligence from its partners and from its frontline soldiers, and was ready for “any kind of provocation”.

On Friday, the US also accused North Korea of supplying “an inital arms delivery” of missiles and rockets to the Russian mercenary group Wagner, which is fighting on behalf of the Kremlin in eastern Donbas. North Korea and Wagner have denied the report.

Asked how Zelenskiy was bearing up as the first anniversary of Moscow’s invasion loomed, Yermak said: “He’s OK.” He added: “Of course he’s working a lot. For him this is normal. He has worked his whole life. He’s a responsible person and deeply involved in everything: weapons, military strategy, energy and economic issues. He’s the best choice of the Ukrainian people.”

A former film producer and lawyer, Yermak joined the presidential administration in 2019 after Zelenskiy’s landslide election victory. Early the following year he became chief of staff. He described his boss as the “best president” in the “current history of Ukraine”.

Russia’s unprovoked invasion, he said, had propelled Zelenskiy to a level of extraordinary global acclaim: “Now Ukraine is the leader of the free world and the leader of our region. We have a strong military. We are liberating our territory and we are fighting the so-called second biggest army on the planet.”

Yermak concluded: “There are terrible tragedies: we are losing the best people. But we will definitely win.”