NATO’s top official, visiting Kyiv, says Ukraine’s ‘rightful place’ is in the alliance.

Jens Stoltenberg, the secretary general of NATO, said on Thursday that Ukraine’s “rightful place” was in the Atlantic alliance as he visited Kyiv for the first time since Russia’s invasion nearly 14 months ago.

Mr. Stoltenberg’s visit was not previously announced, a practice that, because of security concerns, is common for top international officials making trips to Ukraine. His trip was seen as a show of support for Ukraine as the country’s military prepares for an anticipated counteroffensive against Russia.

“I am here today with a simple message: NATO stands with Ukraine,” Mr. Stoltenberg said at a joint news conference with the Ukrainian president, Volodymyr Zelensky, after the pair had held talks. Mr. Stoltenberg said the issue of Ukraine’s NATO membership would be “high on the agenda” at a NATO summit in Vilnius, the Lithuanian capital, in July.

“Let me be clear: Ukraine’s rightful place is in the Euro-Atlantic family. Ukraine’s rightful place is in NATO, and over time, our support will help you make this possible,” said Mr. Stoltenberg, who was pictured paying his respects to fallen soldiers at the Wall of Remembrance, a memorial in Kyiv, on Thursday.

Mr. Stoltenberg said in February that Ukraine “will become a member of our alliance” but that it was a “long-term” prospect.

Mr. Zelensky, who has been invited to attend the NATO summit in Vilnius, said it was important that Ukraine be invited to join the alliance.

“There is no objective barrier to the political decision to invite Ukraine into the alliance,” Mr. Zelensky said.

Ukraine is not a member of NATO, but the alliance helps to coordinate Kyiv’s requests for nonlethal assistance and supports deliveries of humanitarian aid. Some NATO members, such as the United States, are the largest providers of military assistance to Ukraine.

There is division among NATO countries about whether Ukraine should be offered any kind of detailed “road map” toward membership at the Vilnius summit.

Dmitri S. Peskov, the Kremlin spokesman, told reporters on Thursday that it was “undoubtedly” still one of the goals of Russia’s invasion to prevent Ukraine from joining NATO.

“Otherwise it would pose a serious, substantial threat to our country and its security,” he said.

Mr. Stoltenberg’s trip comes a day before U.S.-led talks at Ramstein Air Base in Germany with top defense officials from more than 40 nations, a collective known as the Ukraine Contact Group. Many of those countries are NATO members. The group has met regularly at the base for the past year to discuss and coordinate military and humanitarian aid for Ukraine.

Those talks will most likely focus on plans to send more arms to Kyiv, which has said for months that its troops are short of ammunition and using artillery shells faster than allies can produce and supply them. Those claims were supported by leaked American intelligence documents that began circulating widely this month.

At the news conference on Thursday, Mr. Zelensky said that he had asked Mr. Stoltenberg for his help to “overcome the reluctance” of some countries to provide Ukraine with more advanced weaponry.

Ukraine is preparing for an expected counteroffensive that could try to drive a wedge through Russian-occupied territory along the southern coasts of the Black and Azov Seas, near Crimea, or look to push Russian forces back in the eastern region of Donbas — or both.

As part of his trip to Ukraine, Mr. Stoltenberg visited Bucha, a town north of Kyiv where dozens of civilians were brutally killed by Russian soldiers last year. Mr. Stoltenberg said he was “deeply moved” by what he saw there.

Carly Olson and Ivan Nechepurenko contributed reporting.