A suicide bomber has killed herself and possibly others in the centre of the Chechen capital Grozny. Reports are still confused, but some sources said the middle-aged woman blew herself up next to a police car, killing at least two officers. Others say there were three policemen in the car which was completely destroyed. Yet more reports say no-one was killed, only injured.Violence has been rising in Chechnya after a period of relative calm. President Medvedev has warned that Moscow is struggling to contain an Islamic insurgency in all levels of Chechen society.