The amount of explosives discovered in Serbia last week would not have been enough to destroy the Balkan Stream gas pipeline, prompting an expert to conclude it was probably a Russian intelligence plot aimed at influencing Hungary’s impending election.

A former Ukrainian major general and a munitions specialist told the Guardian calculations made by his company showed the 4kg of explosives recovered by Serbia’s military security agency in Kanjiža could not have seriously ruptured the pipe.

Experts from his firm, Andromeda, analysed the steel and polypropylene connection, which carries Russian gas to Hungary, passing through Turkey, Bulgaria and Serbia, and calculated the amount of explosive they believed to cause serious damage.

To succeed, a significantly greater amount would have been required, Mykola Zentsev said, supplying an estimate in private. “Four kilograms is not sufficient to put the gas pipeline to a standstill,” said Zentsev.

Even if optimally placed, 4kg of plastic explosive “would likely result only in localised damage or limited penetration, which could be repaired within a few days without causing long-term disruption of supply,” he added.

“This does not align with the objective of a classical act of sabotage, which aims to disable infrastructure for weeks or months,” Zentsev concluded, supporting “the conclusion that the incident was likely a provocation”.

On Sunday, Hungary’s prime minister, Viktor Orbán, said he had been informed by Serbia’s president, Aleksandar Vučić, about the discovery of the explosives. Hungary’s foreign minister, Péter Szijjártó, hinted that Ukraine could be responsible in what he described as “an attack on our sovereignty”.

The incident was picked up widely in the media before Hungary’s election on Sunday in which the pro-Russian Orbán is lagging in the polls and fighting for his political survival.

Péter Magyar, the leader of Hungary’s opposition, accused Orbán of “attempting to instil fear in his own people through false-flag operations” and following “the advice of Russian agents”. Ukraine denied being involved, a conclusion endorsed by the chief of Serbia’s Military Security Agency, responsible for the investigation.

Zentsev argued that, in his opinion, “the primary beneficiaries are likely the current Hungarian government, which gains an additional political advantage ahead of elections, and Russia, which seeks to use such incidents to discredit Ukraine in the eyes of the civilised world”.

Under Orbán, Hungary is one of the few EU countries that has chosen to remain close to Russia, buying its gas and oil. Budapest also blocked the approval of a €90bn loan to Ukraine in March after a dispute with Kyiv over repairs to the separate Druzhba oil pipeline, a section of which runs through Ukraine into eastern Europe.

Serbia’s Vučić said last Sunday that the explosives could have “endangered many lives” and caused significant damage to the Balkan Stream pipeline. They were found in two backpacks in Kanjiža, “a few hundred metres from the gas pipeline”.

However, Zentsev said from the public evidence it did not appear any effort had been made to place the explosives on the pipeline itself – and the Ukrainian, close to the country’s security services, said he believed that the incident was probably a false-flag operation conducted by Russia’s GRU military intelligence.

“This meets the standards of the GRU,” said Zentsev, reflecting the incident’s military dimension. Last month, Magyar accused Orbán of inviting GRU agents to help him with his attempted re-election. The Russian embassy in Budapest denied this, describing suggestions of GRU involvement as “openly false information”.