MEXICO CITY — President Enrique Pena Nieto sought to calm tensions Monday over the still-undecided election for governor of the key Mexican border state of Baja California after both sides claimed victory and authorities said mistakes were made in preliminary vote counts.

Complaints over the election in Baja and other states have led the conservative National Action Party to suggest it could pull out of an agreement known as the Pact for Mexico that has become a centerpiece of Pena Nieto's administration.

"It is now up to all candidates and political parties to abide by the decision expressed by citizens at the polls," Pena Nieto said Monday, adding that the vote "confirms the strength and validity of our democracy, but also makes clear there are areas of opportunity to perfect the system."

The preliminary count from Baja California, with about 97 percent of the vote, showed National Action's Francisco "Kiko" Vega ahead with a nearly 3 percentage point lead. But because of technical errors, that count "should not be considered reliable," said election council spokeswoman Helga Casanova. The more thorough official count will begin Wednesday and conclude Sunday.

Vega, who ran in a coalition with the leftist Democratic Revolution Party, had earlier claimed victory, as did the PRI's candidate, Fernando Castro Trenti.

Baja California is especially important to National Action, which has held the governorship since 1989, when its victory was the first recognized opposition win in Mexico's modern history — a democratic milepost for a country dominated by Pena Nieto's Institutional Revolutionary Party, the PRI, from 1929 to 2000.

National Action lost the presidency itself to the PRI last year, but its leaders joined other major parties in signing the pact to cooperate with Pena Nieto in passing education and telecommunications reform laws. Important challenges remain in tax and energy reform.

But National Action officials allege the PRI is returning to its strong-arm tactics of the past, undermining their ability to cooperate.

"We are seeing two realities," National Action leader Gustavo Madero said.

"The Pact for Mexico is very civilized, very advanced policy, but on the other hand, when there are elections, it's back to acting like the 1970s or 80s," Madero said, referring to an era when the PRI ruled through vote fraud and handouts.

Pena Nieto urged continuing support for the pact, saying his government is committed to "continue the dialogue and agreements with all political forces to achieve the reforms needed to consolidate Mexico's democracy."

PRI leader Cesar Camacho brushed off criticisms of Sunday's election, saying the voting in most states appeared to be fair. He alleged that some voters were being intimidated in National Action-led Baja California and that someone had thrown a gasoline bomb at the home of a PRI municipal candidate.

Elections were also held Sunday for state legislators and mayorships in 13 other states after violence-marred campaigns. At least nine candidates, party officials or their family members were killed and others reported being kidnapped or shot at in the runup to the vote.

A young political activist was shot to death on election day in the Gulf coast state of Veracruz and Camacho claimed that he was a PRI supporter.

The causes of most of the attacks are still uncertain. Some fear that drug gangs are asserting their power. Others fear that candidates are being targeted by their rivals.

In local races, the PRI appeared to be winning the mayorship of the border city of Tijuana, while National Action was ahead in Mexicali, the Baja California state capital. Further east along the border, National Action was ahead in the cities of Nuevo Laredo and Matamoros.

To the south, National Action led in the colonial city of Oaxaca, while the PRI claimed to have won the mayorship of the resort city of Cancun.

In the Veracruz state capital of Xalapa, Morris — a cat whose owners ran him as a write-in candidate for mayor to illustrate disgust with the country's politicians — may have won several thousand votes. While electoral authorities simply list write-in votes in a column labeled "unregistered," and don't break down who they were for, there were about 3,400 votes in the column by early Monday. That was about 3.5 percent of the votes counted up to that point. No other city in the state showed anywhere near that level of unregistered votes.

The cat's campaign managers — his owners — asserted in a statement that his real number of votes may have been 8 percent or more of the total, because many precincts also appear to have listed votes for the cat as "void," a column that included about 5,400 more votes, rather than "unregistered." That would have placed the black-and-white feline in fourth place in the race, ahead of six other candidates.

Hundreds of voters sent photos of their ballots to the cat's web site, showing their voting cards marked "Morris" and "Morris The Cat."