Mexico's former first lady Margarita Zavala, whose husband Felipe Calderon launched the country's controversial militarized drug war, plans to run for president in 2018.

Zavala, a 47-year-old former federal lawmaker, said she would seek the nomination of the conservative National Action Party (PAN) just a week after it was clobbered in midterm elections.

"We haven't started the campaign but it's important to signal my intention," Zavala told Radio Formula on Monday, a day after posting a video announcing her plans.

This came after her party finished second in the vote for the 500-member lower house of Congress with 21 percent in June 7 elections, down from 26 percent in 2012.

President Enrique Pena Nieto's Institutional Revolutionary Party finished first with 29.2 percent.

Calderon's 2006-2012 presidency was marked by his decision to deploy troops to combat drug cartels, a move that coincided with a surge in violence that left tens of thousands of people dead.

After 12 years of PAN presidencies, Pena Nieto was elected in 2012, bringing the PRI, which ruled for most of the 20th century, back to power.

Asked whether her husband's security strategy had been the right one, Zavala said: "I think so, yes, in the sense that it is seen in a completely, comprehensive way."

"They will always ask me these questions. The country is in a different situation, and I'm a different person with the six years of experience (as first lady), with the strength of having someone who knows and was president," she told Radio Formula.

Zavala criticized Pena Nieto's fiscal reform, which she said had left families with less money, and called for the country to hold a second round in presidential elections.

Calderon won in 2006 by less than one percentage point against leftist candidate Andres Manuel Lopez Obrador, who refused to concede and led protests that paralyzed Mexico City.

Pena Nieto won in 2012 with 38.2 percent of the vote, compared to 31.6 percent of Lopez Obrador, who cried foul and again refused to concede.

Lopez Obrador, a former Mexico City mayor, plans to run again in three years.

"A second round would remove many confrontations," Zavala said.