By Krisztina Fenyo and Gergely Szakacs

BUDAPEST, March 15 (Reuters) - Hungary's feuding political parties gathered for a key show of force on Sunday as ‌an acrimonious campaign between right-wing Prime Minister Viktor Orban and centre-right challenger ‌Peter Magyar entered a pivotal stage ahead of an April 12 election.

In power since 2010, Orban faces ​what could be his toughest bid for re-election after three years of stagnation, a surge in the cost of living and the rise of a pro-European Union rival seen by many as a viable alternative.

Orban's Fidesz party and Magyar's Tisza were both ‌due to stage large-scale marches ⁠in Budapest to mark Hungary's March 15 national day and rally their supporters, with most surveys showing Tisza ahead by a ⁠wide margin.

Orban has cast the vote as a choice between war and peace, accusing his rivals of plotting to drag Hungary into the war raging in neighbouring Ukraine ​since Russia's ​February 2022 invasion, accusations which the opposition ​has denied.

But Orban's messages still resonated ‌with supporters gathering in the streets of Budapest and planning to march to parliament to attend a speech by the veteran nationalist leader.

"Hungarians, young or old should not be sent to the front lines, because this is a senseless war," said Maria Erdelyi, who attended the rally. "This is only about money and nothing else."

Orban ‌has long been at loggerheads with the EU ​over Ukraine, among many other issues. Defying Brussels, ​he has maintained cordial ties ​with Moscow, refuses to send weapons to Ukraine, and says Kyiv ‌can never join the EU.

Jozsef Lados ​called Orban "Europe's best politician", ​saying Hungary should stick with him instead of betting on Magyar, whom he described as an "adventurer".

Magyar has dismissed Orban's campaign as laughable "propaganda", but Tisza has ​trodden cautiously on Ukraine, ‌saying it opposes any fast-track EU accession for Kyiv and that it ​would put the issue to a binding referendum if it wins ​power.

(Reporting by Gergely SzakacsEditing by Gareth Jones)