Russian President Vladimir Putin on Friday hailed pro-Moscow separatists in eastern Ukraine as “insurgents” battling an army that he likened to Nazi invaders during World War II, and the Ukrainian government raised the prospect of joining NATO as it seeks help to repel what it calls an outright Russian military invasion.

In a statement published on the Kremlin’s Web site early Friday, Putin also urged the separatists
to release Ukrainian soldiers trapped since Monday in the southeastern town of Ilyovaisk. The double-edged statement — couched as a humanitarian gesture but perhaps aimed at helping the rebels consolidate control — came a day after the government in Kiev said Russian soldiers, tanks and heavy artillery had begun rolling into the region to help the separatists reverse recent Ukrainian military gains.

Ukrainian Prime Minister Arseniy Yatsenyuk said Friday that Ukraine may seek to join NATO, announcing the submission of a bill to parliament that would repeal the country’s “non-bloc status,” the Interfax news agency reported.

A Ukrainian military spokesman, Col. Andriy Lysenko, told reporters that Russia continues to send troops and materiel across the border. He said the force includes tanks bearing inscriptions such as “We are going to Kiev.”

“I assure you that on our shells we won’t have any messages like ‘to Moscow’ or ‘on to Moscow,’ ” Lysenko said. “We are not aggressors. We’re just trying to liberate Ukrainian lands.”

Lysenko said the Ukrainian army, after retreating from the southeastern coastal town of Novoazovsk, was ready to defend the key port city of Mariupol, about 28 miles farther west on the Sea of Azov.

Putin did not answer accusations by the Ukrainian government and the West about Russia’s military presence in southeastern Ukraine.

Instead, he praised the separatists as “insurgents” who had undermined “Kiev’s military operation, which threatened lives of the residents of Donbas and has already led to a colossal death toll among civilians” — a reference to the eastern Ukrainian region known as the Donets Basin, or Donbas, whose unofficial capital is rebel-held Donetsk.

Ukraine’s military responded quickly, saying that Putin’s call for an exit corridor for encircled Ukrainian troops showed that the separatists are “led and controlled directly from the Kremlin.”

Pro-Russian separatists said they would comply with the Kremlin’s request, but it was unclear whether Kiev would accept the offer.

At a youth forum later Friday, Putin said Ukrainian President Petro Poroshenko had agreed to a prisoner swap that would include sending 10 captured Russian paratroopers back to Russia.

An advocacy group called Soldiers’ Mothers has been pressing Russian authorities for answers on the fate of troops believed to be fighting in Ukraine. Russia responded by putting the Soldiers’ Mothers of St. Petersburg on a government list of foreign agents.

Russian military allegedly enters Ukraine and attacks its forces.

In the same appearance, Putin said the recent Ukrainian offensive against pro-Russian rebels reminded him of “the events of the Second World War, when the Nazi occupiers, the troops, surrounded our cities — for example, Leningrad — and point-blank shot at these settlements and their inhabitants.” He added: “It’s awful. It’s a disaster.”

Although Putin skirted the issue of Russian military involvement in Ukraine, his remarks directly addressing the separatists and his disparaging comments about Ukrainian forces served to escalate the rhetoric surrounding the crisis at a time when Moscow and Kiev are supposed to be talking about prisoner swaps, humanitarian convoys and other matters.

Ukraine’s president Petro Poroshenko is scheduled to meet in Brussels today with top European leaders to discuss the situation in Ukraine.

Russian and Ukrainian border security services are also expected to meet at the Nekhoteyevka checkpoint in the Belgorod region of Russia, near to the Ukrainian region of Kharkiv, to discuss the situation along the Russian-Ukrainian border, and strategies to prevent militants and military hardware from crossing back and forth.

Putin also said that Ukraine should not fear federalization, asserting that Russia itself would be moving further in that direction, possibly by shifting some central government authorities to Siberia. That declaration comes barely two weeks after activists calling for more federalism in Siberia were detained and protests on the subject were banned.

However, Russia would not “meddle” with Ukraine’s internal affairs, Putin added.

U.S. officials said privately Thursday that they consider the Russian show of military force this week tantamount to an invasion. Speaking at a news conference, President Obama did not use the term but said it was clear the uprising in eastern Ukraine was not “homegrown.”

“The separatists are backed, trained, armed, financed by Russia,” he said.

In a response Friday, Russia’s Foreign Ministry again accused the United States of hypocrisy — this time for what it called U.S. disregard for civilians in eastern Ukraine.

“In any other conflict, whether in the Middle East, Africa or anywhere else, the West has consistently opposed actions causing harm to civilians,” the ministry said on its Web site. “It is only in relation to southeastern Ukraine that it holds a diametrically opposite line, in gross violation of international humanitarian law.”

A total of 2,593 people, including civilians, have been killed in the fighting in eastern Ukraine since mid-April, a senior U.N. human rights official said Friday.

“The trend is clear and alarming,” Ivan Simonovic, U.N. assistant secretary general for human rights, told journalists in Kiev. “There is a significant increase in the death toll in the east.”

Simonovic said the number would be close to 3,000 if the 298 victims of downed Malaysia Airlines Flight 17 were counted. Civilian casualties would continue to rise “as each side increases its strength, through mobilization, better organization, or the deployment of new fighters and more sophisticated weapons and support from outside,” he said.

Simonovic had sharp words for both sides.

“Armed groups continue to commit abductions, physical and psychological torture,” he said of the separatists, whose tactics he said were aimed at terrorizing the population under their control. But he added that the United Nations has also heard “disturbing reports of violations committed by battalions under government control.”

Russia’s Foreign Ministry criticized the U.N. official as repeating “fabrications against the militia forces of Donetsk and Luhansk” but commended him for addressing “the criminal actions of the Ukrainian army” — although the ministry maintained that his report did not go far enough.

“The mission was forced to admit the obvious,” Foreign Ministry spokesman Alexander Lukashevich said.

Branigin reported from Washington. Annie Gowen in Kiev, Anne Gearan and Karen DeYoung in Washington and Daniela Deane in Rome contributed to this report.