Bulgarian Prime Minister Kiril Petkov (L) meets with Ukrainian President Volodymyr Zelensky in Kiev on April 28, 2022.

Politico newspaper reported on Wednesday that Bulgaria secretly provided Ukraine with fuel and weapons during its war with Russia as Kiev's diesel reserves and Soviet-era ammunitions were hitting a critical low.

"Salvation came from an unexpected quarter: Bulgaria," the news site said.

German media outlet Die Welt carried out exclusive interviews with Ukraine's Foreign Minister Dmytro Kuleba, former Bulgarian Prime Minister Kiril Petkov, and his finance minister, Assen Vassilev, whom Politico cited in its report.

According to the news site, citing Welt interviews, the Bulgarian Prime Minister had to keep the supplies secret because of pro-Moscow politicians in his government, "including among his coalition partners."

Petkov also sacked his Defense Minister who praised Russia's role in the war, but at the same time did not publicly say that Bulgaria would use its stock of Soviet weapons to support Kiev.

"In public, at least, [Bulgarian PM] Petkov sought to play down any idea that Bulgaria — despite considerable stocks of Soviet-era weaponry — would step up and arm Ukraine," noted Politico.

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The report added that now, given that Petkov and Vassilev are part of the opposition and are seeking to regain power in the next elections, they have decided to break their silence and disclose the true extent to which Bulgaria was invested in the war in Ukraine last spring.

"While the Socialist Party in Sofia called Bulgarian arms deliveries to Ukrainian forces a “red line,” Petkov’s officials avoided government-to-government transactions and used intermediary companies in Bulgaria and abroad to open up supply routes by air and land through Romania, Hungary, and Poland," the media outlet said.

“We estimate that about a third of the ammunition needed by the Ukrainian army in the early phase of the war came from Bulgaria,” Petkov disclosed to Welt as reported by Politico.

When Petkov traveled to Kiev on April 28 to pledge support for Ukrainian President Volodymyr Zelensky, he didn't have much to offer, at least not officially, according to the newspaper.

The report also revealed that the diesel supplied by Bulgaria to Ukraine was processed in a refinery belonging to Russia's Lukoil located in the Black Sea.

“Bulgaria became one of the largest exporters of diesel to Ukraine and at times covered 40 percent of Ukraine’s needs,” former Finance Minister Vassilev said to Welt.

Ukrainian Foreign Minister Dmytro Kuleba told Welt that his country was on the verge of running out of ammunition only two months into the war, adding, “We knew that Bulgarian warehouses had large quantities of the ammunition needed so President [Volodymyr] Zelenskyy sent me to obtain the necessary material.”

On Monday, Bulgarian authorities rebuked reports that the country had provided NATO allies with Su-25 aircraft that would later be sent to Kiev's forces.

The denial came in response to a Bloomberg report on Sunday stating that Ukraine had received 14 Su-25 aircraft purchased by NATO member states from Bulgaria and delivered to Ukraine, quoting a Dutch defense analysis website Oryx.

Last year, Bulgaria witnessed numerous demonstrations in the capital, Sofia, to protest the supply of weapons to Ukraine, stressing that "Bulgaria should in no way be involved in this conflict."