Lashawn Merritt

The Americans, for whom 400m individual world champion Lashawn Merritt ran the final leg, timed 2min 58.71sec while Jamaica took silver (2:59.88) and Russia the bronze (2:59.90).

The 27-year-old, who won his previous title in 2009 a year after winning Olympic gold, posted the fastest time of the year of 43.74 seconds to take gold while compatriot Tony McQuay ran a personal best (44.40sec) for second place and Luquelin Santos of the Dominican Republic was third (44.52sec).

Double amputee Oscar Pistorius saw his world 400m dream extinguished on Monday as defending champion LaShawn Merritt eased into the final just a month after returning from a drugs ban.

Double amputee Oscar Pistorius on Sunday reached the world championships 400m semi-finals as defending champion LaShawn Merritt also qualified - a month after returning from a drugs ban.

Olympic 400m champion LaShawn Merritt of the United States has been suspended after testing positive for an anabolic steroid contained in an over-the-counter penis enlargement product.

The Americans, for whom 400m individual world champion Lashawn Merritt ran the final leg, timed 2min 58.71sec while Jamaica took silver (2:59.88) and Russia the bronze (2:59.90).

The 27-year-old, who won his previous title in 2009 a year after winning Olympic gold, posted the fastest time of the year of 43.74 seconds to take gold while compatriot Tony McQuay ran a personal best (44.40sec) for second place and Luquelin Santos of the Dominican Republic was third (44.52sec).

Double amputee Oscar Pistorius saw his world 400m dream extinguished on Monday as defending champion LaShawn Merritt eased into the final just a month after returning from a drugs ban.

Double amputee Oscar Pistorius on Sunday reached the world championships 400m semi-finals as defending champion LaShawn Merritt also qualified - a month after returning from a drugs ban.

Olympic 400m champion LaShawn Merritt of the United States has been suspended after testing positive for an anabolic steroid contained in an over-the-counter penis enlargement product.