Rebecca Blackwell, Associated Press
President Enrique Pena Nieto adjusts his microphones as he arrives at a press conference to express his outrage over the recent disappearance of 43 students in Guerrero State following a violent confrontation with the police, in Mexico City, Monday, Oct. 6, 2014. Guerrero state officials worked Monday to determine whether 28 bodies found in a clandestine grave are students who were attacked by police suspected of drug gang links in the southern state of Guerrero.

MEXICO CITY — Since taking office nearly two years ago, President Enrique Pena Nieto has sought to project an image of Mexico on the move, beating back chronic drug violence and pressing ahead with historic constitutional and economic reforms, even offering to contribute soldiers to UN peacekeeping missions in other parts of the globe.

The problem is that, back home, Mexico's grotesque cycle of violence continues, with soldiers and police implicated in recent atrocities. Pena Nieto's determination to focus on Mexico's moment has been derailed by Mexico's mess.

International human rights groups are calling the massacre of 22 suspected gang members in southern Mexico this year a test case for the president, and the world is demanding answers in the forced disappearance of 43 teachers' college students, who are feared to be buried in mass graves discovered after they vanished Sept. 26.

Pena Nieto, unusually, addressed the violence twice this week as everyone from outraged Mexicans to the United Nations and the U.S. State Department called for a full accounting in both mass killings.

He said he has exhorted his security cabinet to step up the investigation.

"This tarnishes the collective national effort we have to truly turn Mexico into a country of greater progress and development," he said, referring to the disappearance of the 43 students of the school in Ayotzinapa.

Pena Nieto until now had left security to his interior minister as the administration restricted the release of information and downplayed drug-related crime.

The macabre headlines are not what Pena Nieto was hoping for during a period in which his security forces nabbed two top drug traffickers and the president was awarded the Global Citizen Award by a U.S. think tank. In the case of the missing students, many of the bodies in the mass grave were burned. One victim of the police violence had his skin peeled from his skull. More than two dozen local police have been arrested in the case.

"It has become increasingly evident that in the process of not allowing this single issue to hijack this administration, he has made the mistake of ignoring it altogether," said Tony Payan, director of the Mexico Center at Rice University's Baker Institute for Public Policy.

Pena Nieto took office vowing to change the narrative after his predecessor's bloody war on drugs, portraying Mexico as ready to lead and as fertile ground for foreign investment. His administration has pushed through reforms to the education system, changed the tax code and opened the energy sector to more foreign investment, among other achievements. He can also point to a string of high-profile drug arrests including that of Juarez cartel leader Vicente Carrillo Fuentes, whose capture was announced Thursday, and Hector Beltran Leyva, who was apprehended last week while eating fish tacos in a central Mexico seafood restaurant.

But even those successes have come with grim side effects. As the major drug organizations have been broken up, smaller and often more-violent bands have taken their place, causing a spike in non-drug crimes that more directly affect citizens, such as kidnapping and extortion. The students in the southern state of Guerrero allegedly went missing at the hands of corrupt police working with the Guerreros Unidos, which was born out of the breakup of the once-powerful Beltran Leyva cartel.

The mayor of Iguala, where the students disappeared, is on the run amid accusations he and his wife were linked to the drug gang and to killings, allegations that date back at least to last year.

Some are calling this the biggest crisis so far of the Pena Nieto administration, a watershed moment similar to past scandals that led to the establishment of the National Human Rights Commission and the dismantling of Mexico's earlier organization for political spying.

"This is a moment for new ideas, not just telling us to all to behave well," Milenio newspaper columnist Carlos Puig wrote Friday of Pena Nieto's response so far. "It's time for something much more serious that just 'coordination.' "

Meanwhile, the government have given a new version of what happened when soldiers encountered alleged gang members June 30 in Mexico State, where a witness told reporters that 21 people were killed after surrendering to soldiers.

Murillo said Friday the majority of the 22 alleged criminals killed that day had already died in a shootout, but that at least eight were still alive when three soldiers finished them off. The soldiers have been charged with murder.