MEXICO CITY (Reuters) - Mexican presidential frontrunner Andres Manuel Lopez Obrador extended his lead to nearly 17 points over his nearest rival ahead of the July 1 vote, according to a poll published on Sunday.

FILE PHOTO: Leftist front-runner Andres Manuel Lopez Obrador of the National Regeneration Movement (MORENA) speaks to supporters during a campaign rally in Uruapan, in Michoacan state, Mexico, June 8, 2018. REUTERS/Alan Ortega

The survey by polling firm Consulta Mitofsky showed Lopez Obrador, running for the third time, had 37.2 percent of support, up from 32.6 percent in May, and 31.9 percent in April.

Second-place Ricardo Anaya, the candidate of the “For Mexico in Front” coalition of three parties from the right and left, saw his backing fall slightly to 20.3 percent, versus 20.5 percent in the previous survey.

Ruling party candidate Jose Antonio Meade rose to 17.1 percent support from 14.5 percent support in May.

The polling reflects the unpopularity of the ruling Institutional Revolutionary Party (PRI) in the bloodiest presidential race of recent history.

On Friday night, Fernando Puron, a congressional candidate for the PRI and a former mayor of Piedras Negras, Coahuila state, was shot in the back of the head as he was greeting supporters just after leaving a debate, according to footage from a security camera.

Puron’s death was the first for a candidate running at the federal level, bringing to 112 the number of candidates, politicians or office holders killed since nationwide campaigning began in September, according to Etellekt, a security consultancy based in Mexico City.

In the poll, independent candidate Jaime Rodriguez rose slightly to 3.2 percent support, taking fourth place in the absence of Margarita Zavala, an independent candidate who withdrew from the race in May.

The face-to-face poll of 1000 people, taken between June 3 and 5, had a margin of error of 3.1 percentage points and 22.2 percent of those surveyed expressed no preference.

Most polls have shown Lopez Obrador growing his lead, but some have shown small growth for Anaya.