TEHRAN, Iran — Iran’s highest leader said Wednesday that any disrupters of national elections, which are less than two weeks away, would receive a “slap in the face,’’ underscoring the political tensions lurking behind the vote.

The warning came in a widely publicized speech by the leader, Ayatollah Ali Khamenei, to graduating cadets of the Islamic Revolutionary Guards Corps, the powerful paramilitary force. He emphasized that security is the most important issue of the May 19 election, when Iranians choose a new president and city and village councils.

Ever since unprecedented antigovernment protests after the disputed 2009 presidential vote, elections have become delicate moments in Iran.

The political atmosphere before this year’s election on the surface seems relatively free and open, in part to ensure that many Iranians turn out to vote for a set of strictly vetted candidates. But the candidates still provide significant choices, compared with elections in many other countries in the region.

The incumbent president, Hassan Rouhani, propagates economic and social freedoms. His main opponent, Ebrahim Raisi, the head of the country’s wealthiest religious foundation, opposes many such ideas and wants Iran to become more self-sufficient.

Televised debates this year have been held with new restrictions, in contrast with the 2009 live debates that helped polarize the country.