UPDATE 6-Mexico's Pemex puts blast death toll at 24, blames leak
* Pemex says death toll from blast could still rise
* Pemex CEO says unclear what caused the accident
* Remediation of the site could take up to a year
* Blast also injured 136 people, 13 of them seriously (Updates number of deaths, comments from press conference, president's visit)
By Lizbeth Diaz
COATZACOALCOS, Mexico, April 21 (Reuters) - Twenty-four people died after a leak caused a deadly petrochemical plant blast, and the death toll could still rise, Mexican oil giant Pemex said on Thursday, the latest in a series of fatal accidents to batter the company.
Pemex CEO Jose Antonio Gonzalez Anaya, who traveled to the site of Wednesday's blast near the port of Coatzacoalcos, one of Pemex's top oil export hubs, told local television it was unclear what caused the accident.
The massive explosion at the facility's chlorinate 3 plant in the Gulf state of Veracruz also injured 136 people, 13 of them seriously. Another 18 people were unaccounted for, and one badly damaged part of the plant had yet to be scoured.
"We know there was a leak, what we don't know is why, but everything points to an accident," Gonzalez Anaya said. Continuación...