* PRI chairman calls for 'crusade' against violence
* Killing occurred in area notorious for drug gang activity (Rewrites with reaction, details, background)
A son of the former chairman of Mexico's most powerful political party was found shot dead in a town south of the U.S. border notorious for drug traffickers, as the violence dogging the country struck the ruling establishment.
The body of Jose Eduardo Moreira, son of the embattled ex-chairman of the Institutional Revolutionary Party (PRI) and former Coahuila state governor Humberto Moreira, was discovered near Ciudad Acuna, across the Rio Grande river from Texas, late on Wednesday, the state's government said on Thursday. He had been reported missing several hours before his body was found.
The centrist PRI ruled Mexico continually between 1929 and 2000 and is due to retake power in December, when Enrique Pena Nieto will assume the presidency.
Military reinforcements were sent into Coahuila to assist investigations into the killing, which hit one of the most prominent political families in the PRI and sp arked ou trage among party leaders.
A funeral service was held for Jose Eduardo on Thursday evening and television pictures showed his father breaking down in tears as he bore his son's coffin in Ciudad Acuna.
"I've had to put up with a lot of things, but I can't bear this," Moreira told reporters. "They killed my son. They shot him twice in the head. I expect justice," he added, calling his son a victim of Mexico's struggle with criminal violence.
Around 60,000 people have been killed in turf wars between drug gangs and their clashes with security forces since President Felipe Calderon of the conservative National Action Party (PAN) took office at the end of 2006.
Calderon staked his reputation on a military offensive to bring the gangs to heel. He has captured or killed many of the top bosses, but the violence has increased on his watch.
Pedro Joaquin Coldwell, who replaced Moreira as PRI chairman, said there could be no impunity in Mexico. "We need a crusade against violence with all tiers of government, society and religious organizations taking part," he said.
Pena Nieto has vowed to quickly reduce the violence after he takes power on Dec. 1. He called the killing an "irreparable loss" to the Moreira family in a Tweet, and said the "murder should not go unpunished."
Critics of the PRI, which became a byword for corruption during its long domination of Mexico, say it is partly to blame for the impunity in the country, accusing it of having made deals with drug gangs in the past to keep the peace.
Jose Eduardo, who was in his twenties, worked for the Coahuila government now led by his uncle, Ruben Moreira.
Ciudad Acuna is a key transit point for cartels running drugs to Texas. It was not immediately clear if Jose Eduardo Moreira's murder was linked to organized crime in the city.
Some media reports said the killing may have been a revenge attack by the brutal Zetas gang on the Moreira family for losses suffered in recent clashes with security forces.
Humberto Moreira stepped down as PRI chairman in December due to a scandal surrounding a massive increase in Coahuila's debt when he was governor between 2005 and 2011.
Coahuila has become one of the states worst hit by drug violence. Though the number of killings nationwide linked to organized crime has eased somewhat this year, the death toll has surged toward its highest level under Calderon in Coahuila.
Calderon also condemned the killing, saying that he "deeply regretted this cowardly murder."