Viktor Orbán and his centre-right rival, Péter Magyar, have traded accusations of enlisting foreign interference in a high-stakes election that polls suggest could mark the end of the nationalist Hungarian prime minister’s 16 years in power.

As the two leaders’ campaigns entered their final stages before this weekend’s vote, which is being watched as keenly in Brussels, Moscow and Washington as in Budapest, Orbán said on social media on Friday that his opponent would “stop at nothing to seize power”.

Magyar and his Tisza party, which according to most polls holds a comfortable double-digit lead over Orbán’s far-right Fidesz, were “colluding” with foreign intelligence and threatening the ruling party’s supporters with violence, the prime minister alleged.

“This is an organised attempt to use chaos, pressure, and international vilification to call into question the decision of the Hungarian people,” Orbán said, adding that Hungary needed “unity and security” and change would “threaten all we have built together”.

Magyar – a former Fidesz loyalist who broke away from the ruling party two years ago, accusing it of corruption and propaganda – hit back, saying Orbán would be “removed by the same people … he has abandoned and betrayed: millions of Hungarians”.

Magyar added in a social media post: “The ongoing election fraud carried out for months by Fidesz, along with criminal acts, intelligence operations, disinformation and fake news cannot change the fact that Tisza is going to win this election.”

He urged voters “not to fall for provocation” and said Orbán, whose transformation of Hungary into a self-styled “illiberal democracy” has inspired far-right leaders and led to fierce clashes with the EU, must “accept the Hungarian people’s judgment with dignity”.

The populist prime minister, 62, is the EU’s most Moscow-friendly leader, and recent allegations of Russian interference in the ballot, along with revelations that Orbán’s ministers shared confidential EU information with Moscow, have prompted outrage across the bloc.

Government spokespeople have in turn tried to portray the string of leaks revealing Budapest’s close ties with Moscow – including the transcript of a conversation between Orbán and the Russian president, Vladimir Putin – as evidence of foreign interference.

While opinion polls put Magyar ahead, observers warn that the electoral system is complex and districts have been redrawn to favour Fidesz. Some calculate Tisza needs a six-point lead in the national vote just to secure a majority in parliament.

Both candidates held rallies on Friday, with Magyar supporters in Hatvan, about 35 miles (60km) east of Budapest, saying they hoped above all for change from an Orbán era marked by soaring levels of cronyism and corruption and a stagnating economy.

“I really hope there will be some change in Hungary, because we really need it,” said Xenia, who asked not to be fully identified, one of an enthusiastic crowd of several hundred. “After 16 years, there is [finally] some hope, at least for now.”

Asked about Magyar, she said: “We tried to change the regime four years ago, but the candidate wasn’t strong enough. [Magyar] can attract many more people around him. I don’t know if it’s going to work out or not, but this is the first chance we actually have to change something, and it would be foolish not to try.”

Another Magyar supporter, Levente Kohári, said he was particularly frustrated by the state of the Hungarian economy and allegations of misuse of public funds. “I don’t want to pay taxes to … a state where my tax money goes to waste,” he said.

Kohári said he hoped to see the 45-year-old opposition leader adopt a more pro-business platform to help young entrepreneurs like him, with a push towards more supportive regulations and making the most of EU membership.

Meanwhile, about 2,000 Orban supporters gathered in Hungary’s second largest city, Debrecen, a longstanding Fidesz stronghold that is predicted to swing to Tisza on Sunday, as protesters shouted “filthy Fidesz” and “Russians go home”.

“I don’t trust Magyar – from one day to the next he turned and stabbed Fidesz in the back,” said Attila Szoke, a 55-year-old taxi driver.

Orbán’s four successive governments since 2010 have eroded the rule of law in Hungary, packing the courts with judges loyal to him and turning up to 80% of the country’s media into a propaganda machine for himself and Fidesz.

He has fought repeatedly with Brussels, which has suspended billions of euros in EU funding, over policies including on migration, justice, LGBTQ+ rights and aid for Ukraine, which, along with sanctions against Russia, he has consistently blocked.

Under Orbán, Budapest has also become the key EU ally of Donald Trump, whose national security strategy aims to boost forces disruptive to the EU. Trump’s vice-president, JD Vance, was in the Hungarian capital to stump for Orbán this week.

The US president posted overnight on his Truth Social platform: “GET OUT AND VOTE FOR VIKTOR ORBÁN. He is a true friend, fighter, and WINNER, and has my Complete and Total Endorsement. I AM WITH HIM ALL THE WAY!”