Russian President Vladimir Putin said Thursday that attempts by Western countries to exclude Russian energy suppliers will affect the global economy and that European Union countries have no alternative resources.

"Consequences of such a step can become quite painful, first of all, for initiators of such a policy," Putin said during a meeting with top officials on the situation in the Russian oil and gas sector.

Putin claimed that Russian natural gas can't be replaced by alternative resources.

"What is surprising here: so-called partners from unfriendly countries assume that they can avoid Russian energy resources, including natural gas. Its reasonable replacement for Europe doesn't exist. It is possible, but it doesn't exist so far," Putin said. "Everyone understands there is no free volume (of energy resources) on the world market."

Putin said Moscow will redirect its energy eastward, as European countries try to reduce reliance on Russian exports.

"EU countries talk of cutting off energy supplies from Russia, driving up prices and destabilizing the market," Putin said.

Putin said that Russia should embark on building infrastructure for eastward oil and gas exports as the country needs to diversify its energy supplies away from Europe.

Thirty prisoners of war will be returned to Ukraine on Thursday as part of the latest exchange of captives with Russia, according to Ukrainian Deputy Prime Minister Iryna Vereshchuk.

Vereshchuk said in a statement via social media Thursday that, following an order from Ukrainian President Volodymyr Zelenskyy, five officers and 17 servicemen were exchanged, along with the release of eight civilians, including one woman.

"In total, 30 of our citizens are going home today," Vereshchuk said.

Thursday's prisoner swap marked the fourth to take place between the two countries since Russia launched an invasion of Ukraine on Feb. 24.

Nine humanitarian corridors are expected to reopen in eastern Ukraine on Thursday to allow civilians escape heavy fighting, according to Ukrainian Deputy Prime Minister Iryna Vereshchuk.

She said in a statement via social media Thursday that evacuation routes were agreed upon for those traveling by private cars from besieged Mariupol in the Donetsk Oblast, as well as from Berdyansk, Tokmak and Enerhodar in the Zaporizhzhia Oblast -- all of which lead to the southeastern city of Zaporizhzhia.

In the Luhansk Oblast, Vereshchuk said routes were established from the cities of Severodonetsk, Lysychansk, Popasna, Hirske and Rubizhne, leading to the city of Bakhmut in the Donetsk Oblast.

Humanitarian corridors were not reopened the previous day because Russian forces had blocked evacuation buses in the Zaporizhzhia Oblast and violated the cease-fire in the Luhansk Oblast, according to Vereshchuk.

"All this creates such a level of danger on routes that we are forced to refrain from opening humanitarian corridors today," she said in a statement via social media Wednesday.

Russian forces are likely to attack the towns of Kramatorsk and Kostiantynivka in eastern Ukraine, the U.K. Ministry of Defense warned in an intelligence update Thursday.

The towns are both located in the Donetsk Oblast of the disputed Donbas region, where Russian troops are "striking Ukrainian forces in preparation for a renewed offensive," according to the ministry.

"Urban centres have faced repeated indiscriminate attacks from Russia throughout the conflict," the ministry said. "The towns of Kramatorsk and Kostiantynivka are likely to be Russian targets for similar levels of violence."

The railway station in Kramatorsk was the site of rocket attack that killed dozens of civilians trying to evacuate the region on April 8.

"The combination of widespread missile and artillery strikes and efforts to concentrate forces for an offensive represents a reversion to traditional Russian military doctrine," the ministry added. "However, this will require significant force levels. Ukraine's continued defence of Mariupol is currently tying down significant numbers of Russian troops and equipment."

Mariupol, a strategic port city in the Donetsk Oblast, has been under heavy Russian bombardment since the start of the invasion on Feb. 24. Strong resistance from Ukrainian troops have prevented Russian forces from taking full control of Mariupol.

Mariupol has not yet fallen, despite Russia's demands that Ukrainian troops defending the besieged Ukrainian port city surrender, according to Ukrainian Prime Minister Denys Shmyhal.

"There [are] still our military forces, our soldiers, so they will fight until the end," Shmyhal told ABC News' George Stephanopoulos in an exclusive interview Sunday on "This Week."

Mariupol is a strategic city for Moscow because it would allow Russian forces in the south to connect with troops in eastern Ukraine's contested Donbas region. It would also give Moscow a key port.

Although Mariupol remains under the Ukrainian government's control, Shmyhal said the city's residents are suffering.

"They have no water, no food, no heat, no electricity," he said. "They ask all of our partners to support and help stop this humanitarian catastrophe."

-ABC News' Monica Dunn