WASHINGTON (AP) — NATO Secretary-General Jens Stoltenberg told President Joe Biden at an Oval Office meeting on Tuesday that Ukrainians are "making progress” with their counteroffensive, which could bolster their position when there's an opportunity to reach a diplomatic end to the war with Russia.

“The support that we are providing together for Ukraine is now making a difference on the battlefield as we speak,” Stoltenberg said. “Because the offensive has launched, and the Ukrainians are making progress, making advances."

He added, “It's still early days, but what we do know is that the more land that Ukrainians are able to liberate, the stronger hand they will have at the negotiating table.”

Biden said NATO has grown more unified during the Ukraine war and “we’re going to be building on that momentum” when the alliance holds its annual summit in Vilnius, Lithuania, on July 11 and 12.

The White House meeting, the fourth between the two leaders, occurred at a moment of particular peril and uncertainty for the 31-member military alliance.

Ukraine, armed with Western weapons, is in the early stages of a high-stakes counteroffensive against Russia that could significantly reshape a war that began nearly a year and a half ago. NATO wants to continue supporting Kyiv while avoiding being drawn into direct conflict with Moscow.

Russian President Vladimir Putin has claimed that Ukraine is suffering setbacks and the loss of tanks and armored vehicles.

In addition, no consensus has emerged over who will be NATO's next leader. Stoltenberg, a former Norwegian prime minister, plans to step down as secretary general at the end of September. He's held the job since 2014.

Last week, British Prime Minister Rishi Sunak made the case for U.K. Defense Minister Ben Wallace to replace Stoltenberg. Biden also met with Danish Prime Minister Mette Frederiksen, another potential contender.

NATO has expanded since Russia's invasion of Ukraine with the addition of Finland. Sweden has also sought to join, but Turkey, another member of the alliance, has objected.

However, Biden has expressed confidence that the issue will be sorted out and Sweden will become the 32nd country in NATO.

The meeting with Stoltenberg was delayed by a day because Biden got a root canal on Monday. The procedure, which was prompted by dental pain that Biden felt over the weekend, also required the president to skip an event with college athletes.

The night before the root canal, “he was up all night in pain,” first lady Jill Biden said at a political fundraiser in New York City on Monday evening.