Hungary’s prime minister, Viktor Orbán, has accused Ukrainians of plotting to attack his family, as an increasingly bitter standoff between Kyiv and Budapest continues. Orbán and his allies appear to be using the dispute for maximum political gain, before the election due next month that could bring an end to the 16-year rule of his nationalist government.

Orbán released a video on Wednesday night purporting to show him speaking to his daughters on the phone. “I’m sure you’ll see on the news that the Ukrainians have threatened not only me but you as well,” he said, apparently emotional. “My kids and my grandkids … We have to take this seriously but we must not be scared,” he added.

Orbán was apparently responding to the words of Hrihoriy Omelchenko, a retired politician who served in Ukraine’s SBU security service in the 1990s. He issued threats to Orbán in a televised interview earlier this week suggesting vigilantes could hunt the Hungarian prime minister down if he does not change his anti-Ukrainian position.

Earlier, Ukraine’s president, Volodymyr Zelenskyy, had threatened to “give this person’s address to our armed forces” while speaking about Orbán, in comments that reportedly prompted European allies to ask the Ukrainian leader to tone down his rhetoric.

Orbán has long been the most pro-Russian leader of EU nations, leading to messy relations with Kyiv, but as polling has him up to 20 points behind the challenger Péter Magyar and with parliamentary elections approaching next month, the anti-Ukraine campaign in Hungary has gone into overdrive.

The trigger for the latest round of tensions was Ukraine’s claim that it would take several weeks to repair an oil pipeline that transports Russian oil to Hungary, which was reported damaged in a Russian drone attack.

In response, Orbán vetoed further EU sanctions on Russia as well as an additional €90bn loan for Ukraine. Last Friday, in an escalation that shocked Kyiv, Hungary’s anti-terrorism police impounded a convoy of two armoured cars belonging to Oschadbank, Ukraine’s state savings bank, and arrested the seven Ukrainians accompanying it.

The convoy was transporting tens of millions of euros worth of cash – as well as 9kg of gold bars – from Vienna to Kyiv, in what Kyiv said was a normal government cash transfer which the Hungarian authorities had been notified of. Budapest suggested the money was being laundered. The seven men arrested were held incommunicado for more than 24 hours before eventually being driven to the border with Ukraine and deported. The money and gold is still in Hungary.

“Every aspect of the procedure was unlawful, in particular the withholding of legal assistance,” Lóránt Horváth, the men’s Hungarian lawyer, told the Guardian. One of the seven, who suffers from diabetes, was taken to hospital during the interrogation, he said: “He did not know exactly which hospital, as he was transported in handcuffs and with a hood over his head.”

According to a statement from Ukraine’s foreign ministry, the man was taken to hospital after being “forcibly injected with a drug after which his blood sugar level rose sharply and hypertension began”. Horváth said he had no information about a forcible injection, but added that he was only able to speak to his clients by phone, as the Hungarian authorities had denied him access to the men.

The Ukrainian foreign ministry said “psychological and physical pressure was exerted on the detainees” throughout their detention. A security source in Kyiv said the authorities there had been stunned after debriefing the men on their return, claiming that the Hungarians had been trying to pressure the arrested men into making a confession video. “We know that Hungarian counterintelligence can be aggressive, but these seem like Russian-style methods,” said the source.

This week, officials from the two countries continued to trade accusations over the incident. Ukraine’s foreign minister, Andrii Sybiha, wrote: “The mask has slipped … They openly confess to taking hostages and stealing money with the aim of demanding ransom. Such actions must be called by their name: state terrorism.”

His Hungarian counterpart, Péter Szijjártó, called Sybiha’s accusations “pretty pathetic” and said he should instead answer questions that arose from the incident: “Why did they deliver a huge amount of cash to Hungary? What did they want to spend this money on? Is this the money of the Ukrainian war mafia?”

The Hungarian election will take place on 12 April, leaving plenty of time for further escalation. Earlier this week, the Financial Times reported that a Kremlin-aligned thinktank has drawn up plans for a disinformation campaign to boost Orbán’s re-election chances. Orbán has been one of the few EU leaders to call for keeping positive relations with Moscow, and Szijjártó has visited Russia 14 times since the full-scale invasion in 2022.

Orbán has claimed that a win for Magyar would drag Hungary into the war on the side of Ukraine, and has attempted to portray himself as a peace candidate who is neutral in the conflict.

“Is Zelenskyy forming a government, or am I? And if we only have these two options I suggest myself,” Orbán told supporters at a rally on Wednesday evening in the town of Vecsés.