Mexico City: A mayoral candidate in a northern Mexican municipality was shot dead on Monday, the third attack on a politician in less than a week and the latest incident in the run-up to Mexico’s first elections since last year’s presidential vote.

Ricardo Reyes, a candidate for the leftist Citizen’s Movement party, was running for mayor of San Dimas municipality.

He was killed around midday in Tayoltita, a rural mining town in the northwestern state of Durango, a party statement said.

“The cowardly killer of comrade Reyes is part of an alarming climate of violence and impunity, which seems to be aimed at inspiring terror ... before the elections next Sunday,” the statement said.

The state attorney general could not immediately be reached for comment.

Last week, a ruling party candidate for the state legislature in Mexico’s southern Oaxaca state was shot several times and left in critical condition.

That came just two days after police found the body of a top leader of the leftist Party of the Democratic Revolution (PRD), also in Oaxaca state.

It is still unclear who or what groups were behind the three separate attacks.

Fourteen Mexican states will vote Sunday in the first major election since Enrique Pena Nieto’s Institutional Revolutionary Party, or PRI, took power last year.

The PRI, which ruled Mexico with an iron fist for much of the 20th century, was ousted in 2000 by the National Action Party (PAN).

The PAN is on track to retain the key electoral bastion of Baja California next month, according to a poll released last week, in a result that could strengthen a fragile cross-party alliance built by Pena Nieto to re-energise the economy.