Russia-Ukraine updates: 2 US veterans who joined Ukrainian forces missing

Figures show the number of people returning to Ukraine in the past three days is higher than the number of people trying to flee, the State Border Guard Service of Ukraine said on Sunday.

Of the nearly 84,000 people traveling in and out of Ukraine on Saturday, more than half were Ukrainian nationals returning to the country, the Ukrainian authorities said.

More than 46,000 people returned to Ukraine on Saturday while 37,000 people left the country, the Border Guard Service said.

At least 22,000 of those who left the country traveled to Poland while the rest went to Slovakia, Hungary, Romania and Moldova, officials said.

Since the start of the Russian invasion of Ukraine, more than 6 million Ukrainians have fled the country. Since then, more than 1.6 million people have returned to Ukraine, officials said.

-ABC News' Christine Theodorou

Finland's leaders on Sunday said the Nordic country would apply for NATO membership.

"It is a historic day -- of course, we have, for years, been in close partnership with NATO," Prime Minister Sanna Marin said on Sunday.

Marin and President Sauli Niinistö made the official announcement at a press conference in Helsinki, the capital. The Finnish Parliament is now expected to vote on whether to apply.

Marin said she hoped neighboring Sweden would also decide to join the military bloc in the coming days. Decisions made by both countries "will influence and affect the whole of Nordic countries," she said.

Niinistö said Finland has been discussing NATO membership internally for "at least 30 years."

"We have to keep in mind that NATO membership does not change geography, so we will always have that big border -- land and sea -- with Russians behind it," Niinistö said on Sunday.

Russia has "lost momentum and fallen significantly behind schedule" in its offensive on eastern Ukraine's Donbas region, the U.K. Ministry of Defense said.

"Despite small-scale initial advances, Russia has failed to achieve substantial territorial gains over the past month whilst sustaining consistently high levels of attrition," the ministry said on Sunday. "Russia has now likely suffered losses of one third of the ground combat force it committed in February."

Russian forces in late March pulled out of the suburbs north of Kyiv and collected in eastern Ukraine. They began an offensive in April, but have since foundered, the U.K. said.

Low troop morale, reduced combat effectiveness and loss of equipment have all played a role in slowing the Russian advance, the ministry said.

Russian Foreign Minister Sergei Lavrov said the West has declared a "total hybrid war" on Russia and warned that everyone will feel the consequences on Saturday.

"The collective West has declared a "total hybrid war" against us and it is hard to predict how long it will last, but it is clear that everyone, without exception, will feel the consequences," he said at a meeting of the Council for Foreign and Defense Policy on Saturday.

Lavrov added: "We did our best to avoid a direct clash, but if they have challenged us, we, of course, accept it," the minister said. "We are used to sanctions, they have existed nearly forever in one or another kind."