By Lizbeth Diaz

MEXICO CITY (Reuters) - At least 22 suspected gang members were killed southwest of Mexico City early on Monday, the government said, in one of the bloodiest shootouts with security forces since President Enrique Pena Nieto took power.

An Interior Ministry spokesman said the gunfight took place in Tlatlaya on the southern fringes of the State of Mexico, an area that has been plagued by gang violence in the two neighboring states of Guerrero and Michoacan.

A spokesman for federal prosecutors said all the dead were believed to be gang members.

According to Mexican media reports, the shooting started after soldiers came under fire from the suspected gang members, resulting in a gunfight lasting several minutes.

Pena Nieto took office in December 2012 pledging to quell gang violence that has claimed more than 90,000 lives since 2007. Total homicides are down in Mexico since he took over, but the death toll has risen in parts of the country.

The State of Mexico is the country's most populous region and Pena Nieto's home state, and there murders have risen by nearly 14 percent this year from 2013, government data show.

Michoacan has seen a jump in homicides of more than 40 percent this year, in spite of a concerted effort by the government to pacify the state, which was heavily under the control of the Knights Templar drug gang at the start of 2014.

In January, the Mexican government reinforced Michoacan and forged an uneasy alliance with local vigilante groups in a bid to bring the Knights Templar to heel.

However, monthly homicides in Michoacan reached their highest level since 1998 in May of this year, and the government arrested one of the vigilante leaders on Friday.

(Additional reporting by Gabriel Stargardter; Editing by James Dalgleish, Bernard Orr)