Two ships sold by state-owned oil giant Petroleos Mexicanos, or Pemex, to scrap yards in Pakistan and Bangladesh contained hazardous materials, a violation of both Mexican and international law, an environmental group said.

"The arrival of these obsolete vessels, the Sebastian and the De Marz, in South Asia without notice and without first being pre-cleaned of the tons of hazardous materials built into each ship is a clear violation of the UN Basel Convention and Mexican law," Basel Action Network, or BAN, said in a statement.

BAN monitors compliance with the Basel Convention on the transborder shipment of hazardous wastes.

"Mexico has violated its own laws and international law. In accordance with Mexico's obligations under the Basel Convention, these toxic ships must be repatriated immediately," BAN Green Ship Recycling Campaign director Colby Self said. "The governments of Bangladesh and Pakistan must be told to return the ships and under no circumstances allow them to be scrapped on their beaches."

The environmental watchdog group said it first contacted the Mexican Environment and Natural Resources Secretariat in October 2010 to warn officials that Pemex planned to sell the obsolete vessels to foreign salvage yards.

"At that time, the government replied, stating that they had intervened to block the sale of three Pemex tankers and imposed restrictions on Pemex's future sales to prevent the illegal export of the vessels," BAN said.

The environmental group notified the government on April 6 that Pemex planned once again to sell the ships on the grounds that the vessels would continue to be used for maritime purposes.

Pemex's move was "an apparent attempt to bypass the Basel Convention rules on disposal of hazardous waste," BAN said.

"Nevertheless, Mexican officials disregarded BAN's warning and allowed the vessels to depart for alleged re-use, only to sail directly to Pakistan and Bangladesh for scrapping last month," the Seattle-based environmental group said.

"BAN is now calling on the newly elected Mexican Government to take immediate corrective action by repatriating the two vessels to Mexico," the environmental watchdog group said.

Neither the Environment Secretariat nor Pemex have responded officially to the allegations made by the environmental group. EFE