Poland's gas supply arrangement with Gazprom is for 10.2 billion cubic meters (bcm) per year, which covers over half of the country's usage.
Supplies from Gazprom via Ukraine and Belarus would be halted at 8 a.m. (0600 GMT) on Wednesday, according to Poland's state-owned PGNiG, although the country claimed it did not need to draw on reserves because its gas storage was 76 percent full.
Only a few customers have complied with Russian President Vladimir Putin's demand that "unfriendly" countries pay for gas imports in roubles.
"Russia's ultimate goal is not merely to capture Ukrainian territory, but to dismember the entire center and east of Europe and strike a global blow to democracy," Ukraine's President Volodymyr Zelenskiy declared late Tuesday.
Andriy Yermak, his chief of staff, said Russia was "starting the gas blackmail of Europe."
"Russia is attempting to break our partners' cohesiveness," Yermak stated.
Bulgaria, which relies nearly entirely on Russian gas imports, claimed it had met all of its contractual duties to Gazprom and that the proposed new payment scheme was in violation of the agreement.
It has undertaken preliminary talks with Turkey and Greece about importing liquefied natural gas.
Gazprom said it had not yet halted shipments to Poland, but that Warsaw would have to pay for gas in accordance with its new "payment order." It did not respond to a request for comment on Bulgaria.
Thousands of people have been killed or injured as a result of the February 24 onslaught on Ukraine, which has reduced towns and cities to rubble and prompted more than 5 million people to escape to other countries.
Moscow refers to its efforts as a "special operation" aimed at disarming Ukraine and defending it against fascists.
Ukraine and the West say this is a pretext for an unjustified war to capture territory, raising concerns of a larger European confrontation not seen since World War II.
Russia's ambassador to the US has warned the US to cease delivering weaponry to Ukraine, claiming that major arms deliveries from the West are exacerbating the situation.
On Tuesday, more than 40 countries gathered in Germany to discuss Ukraine's defense.
While flying to Tuesday's conference, Mark Milley, chairman of the US Joint Chiefs of Staff, told reporters that the next several weeks in Ukraine would be "very, very significant."
On Tuesday, Germany confirmed the transfer of its first heavy armaments to Ukraine, including Gepard tanks with anti-aircraft guns.
Ukrainian demands for heavy weapons have grown after Moscow relocated its attack to Donbas' eastern part, which is better suited for tank fights than the areas around Kyiv, where much of the previous combat occurred.
According to regional governor Vyacheslav Gladkov, a series of blasts were heard early Wednesday in the Russian city of Belgorod near the Ukrainian border, and a munitions stockpile in the province was on fire.
Gladkov stated that no citizens were injured in the fire that broke out near Staraya Nelidovka settlement. Russia accused Ukraine of using helicopters to attack a fuel store in Belgorod and opening fire on numerous communities in the area earlier this month.
The province of Belgorod borders the Ukrainian districts of Luhansk, Sumy, and Kharkiv, which have all suffered intense conflict since Russia invaded Ukraine two months ago.
Fighting has persisted in Ukraine's eastern and southern regions.
Body armour is worn by Ukrainian farmers plowing their fields in the southern district of Zaporizhzhia, which is close to the front line. Read the entire story here.
According to Interfax news agency, Russia's defense ministry announced its forces had "liberated" the whole Kherson area in southern Ukraine, as well as parts of the Zaporizhzhia, Mykolaiv, and Kharkiv regions. If confirmed, this would be a big step forward for Russia.
According to the city's mayor, Ukrainian officials demolished a massive Soviet-era monument in the heart of Kyiv on Tuesday, which was designed to symbolize friendliness with Russia.
A 27-foot bronze statue on a pedestal portrayed a Ukrainian and Russian worker holding up a Soviet order of friendship. The statue stood beneath a massive titanium "People's Friendship Arch," which was created in 1982 to mark the Soviet Union's 60th anniversary.
"We can clearly see what this 'friendship' entails: the destruction of Ukrainian cities and the deaths of tens of thousands of peaceful citizens. I'm confident that such a memorial now has a completely different meaning "Vitaly Klitschko, the mayor of Kyiv, stated.
On Tuesday, UN Secretary-General Antonio Guterres warned Russia's foreign minister that the organization's resources would be fully mobilized to save lives and rescue people from the besieged Ukrainian city of Mariupol.