Sen. Manlio Fabio Beltrones has decided to drop his bid for the presidential nomination of Mexico's Institutional Revolutionary Party, or PRI, leaving former Mexico state Gov. Enrique Peña Nieto as the only contender.

"I have decided today not to participate in the internal process for the presidential candidacy, opting to be a man who serves the interests of the country and my party, which I dream of seeing renewed and leading the construction of a prosperous and safe new nation," Beltrones said in a statement published Tuesday in several newspapers.

The senator, who was trailing Peña Nieto in the polls, said he pulled out as a "contribution to the PRI victory in 2012" and "not as a sacrifice."

There are those in the PRI "who are in a hurry and claim the need for unity to hold on to privileges to guarantee their personal or group interests," Beltrones said, without identifying anyone.

Now "is not the time for ambition," Beltrones said.

Polls show the PRI, which governed Mexico from 1929 to 2000, regaining the presidency in next year's election.

Mexico will hold its presidential election on July 1, 2012, electing a successor to President Felipe Calderon of the National Action Party, or PAN.

The leading candidates are Peña Nieto, who is now in line to be the standard-bearer of the coalition formed by the PRI, the Mexican Green Party, or PVEM, and Nueva Alianza, former Mexico City Mayor Andres Manuel Lopez Obrador, who heads the ticket of the alliance formed by the leftist Party of the Democratic Revolution, or PRD, the Workers Party, or PT, and the Movimiento Ciudadano.

The PAN, which is going it alone in the election, has not decided on a candidate yet.

Josefina Vazquez Mota, Santiago Creel and Ernesto Cordero are vying for the PAN's nomination.