Mexican security forces on Monday said they seized more than 40 tons of methamphetamine in a raid on a huge illegal drug laboratory in a rural area in the north-west of the country. In addition to the finished product, during the operation they found a quantity of chemicals which they estimate could have produced another 50 tons of synthetic drugs, the army said. The discovery near the town of Rancho Viejo in the north-western state of Sonora was the most significant in Mexico for years. No arrests have been reported. Against the backdrop of the so-called drug war, Mexico is suffering from hig…