Hungarian Prime Minister Viktor Orban has convened an emergency meeting of the National Defence Council after explosives were found near a pipeline that transports Russian gas to Hungary.
The discovery in a border area of neighbouring Serbia comes as Orban's party is badly trailing in opinion polls ahead of crucial elections next Sunday.
Opposition leader Peter Magyar accused him of "panic-mongering" orchestrated by "Russian advisers", days after security experts warned of a possible "false flag" operation that could be blamed on Ukraine.
Orban, an ally of Russian President Vladimir Putin, has resisted EU calls to abandon Russian energy imports since the full-scale invasion of Ukraine.
In recent weeks Hungarian security experts have raised the possibility of a staged operation, either on Hungarian or Serbian territory, intended to arouse enough sympathy for Orban to help his Fidesz party win the election - or to give Orban an excuse to declare an emergency and postpone or cancel the vote.
