Former prime minister Kiril Petkov says he will sue Iliana Yotova over claims she made about him in a TV debate on state broadcaster BNT. He announced the move on social media. Petkov said he has told a team of lawyers to prepare the claim and that work has already begun.

The only head-to-head debate between Yotova and Andrey Gyurov, the two presidential candidates, took place the evening before Petkov's announcement, three days before the runoff. They discussed security in the Black Sea, the war in Ukraine and the contract with Turkey's Botas.

More on this story: Yotova and Gyurov clash over Black Sea, Ukraine and Botas in their only debate

In the debate, Yotova, who was vice president under Rumen Radev, said Petkov was going to betray the national interest in talks with Skopje over the so-called "French proposal", but Radev stopped him. She said Petkov and former finance minister Asen Vasilev cut off Russian gas supplies "overnight", and that this is why the deal with Turkish pipeline company Botas was signed.

Petkov, a former co-leader of We Continue the Change, replied: "See you in court, Ms Yotova! Your lies were ugly, spiteful and damaging to Bulgaria's interests." He says Yotova has lied about him many times and in doing so accused him of treason.

Petkov said that under his government Bulgaria's position on North Macedonia became the position of the whole EU. He called this an undeniable Bulgarian success that Yotova presents as betrayal.

Petkov said the only trip they made together to North Macedonia was to Bitola, not Skopje, to open a Bulgarian club, not for talks on the agreement. As proof, he posted a photo with balloons from the opening and called her claim an easily disproved lie. "Were you saving the 'national interest' in front of the new club's balloons?" he asked.

On Botas, Petkov said Gazprom, not his government, cut off Russian gas. He said the Kremlin asked Bulgaria to pay in roubles, in breach of the contract, and that Bulgaria's refusal to accept this was the reason for the cut-off. Petkov called the request blackmail.

Petkov recalled that President Radev's caretaker government signed the Botas contract, and that Yotova was then his vice president. He called it one of the worst energy contracts in Bulgaria's modern history.