Mexican authorities Thursday broke up a plot to assassinate two brothers, both leftist lawmakers, including the former campaign manager of the runner-up in last year's presidential election.
Mariana Benitez, a senior prosecutor, said an unspecified number of people were detained in a Mexico City hotel over plans to kill Senator David Monreal and his brother Ricardo, who managed Andres Manuel Lopez Obrador's campaign.
Authorities seized weapons, communications equipment and a sport-utility vehicle, "which they planned to use for the attacks," Benitez told a news conference. The raid was conducted "without violence."
She said the suspects came from outside Mexico City and they had confessed to the crime, but the prosecutor did not indicate a motive. An investigation is under way to find any other suspects.
The Monreal brothers were personally notified about the plot and were offered protection, Benitez said. She said intelligence reports led to the arrests.
Lopez Obrador voiced his "solidarity" with the brothers on Twitter and called for quick answers about the plot.
"Smokescreen, intimidation, terror and from whom? The truth must rapidly be known," said the leftist politician and former Mexico City mayor.
Lopez Obrador lost the July 2012 election to Enrique Pena Nieto, the candidate of the Institutional Revolutionary Party (PRI) that had ruled Mexico for most of the 20th century.
The leftist charged that the PRI bought votes to secure victory, but electoral authorities threw out his claim. He had also claimed fraud after losing the 2006 election to Felipe Calderon, whose six-year term ended in December.
Ricardo Monreal, 52, is the coordinator of the Citizen Movement, a small left-wing party in the lower house of Congress, while his 47-year-old brother David is a senator from the Labor Party.
The older Monreal wrote on Twitter that he had endured "difficult hours" but that he was well and had decided to go home to his wife and children after a session in the lower house.
He said he would make a statement on Friday when more information is available.
Mexico has been rocked by a wave of drug-related violence that has left 70,000 people dead since 2006, including several local-level lawmakers and mayors.
The Monreal brothers hail from the central state of Zacatecas, which has not been spared by the drug war.
Ricardo Monreal was governor of the mining state from 1998 to 2004. His younger brother David was mayor of the municipality of Fresnillo from 2007 to 2009.
The Citizen Movement party asked for a thorough investigation.
Ricardo Mejia, a top party official in the lower house of Congress, said Ricardo Monreal left the legislature Thursday afternoon by car and without an escort.
"He is well and with his family," Mejia said. "They are austere people. They don't like to have security or people helping them."