An attack in Chechnya that killed at least nine pro-Moscow police last week was a suicide bombing, a rebel statement said on Monday in the first such claim of responsibility since the Beslan school siege in September. Local media reports said last Friday's attack was caused by a radio-controlled bomb, but a rebel statement posted on the Internet said a single suicide bomber had attacked a column of local troops in a mined car. "He crashed into the column of cars at full speed, destroying three cars and their crews. The fighter was martyred," said the statement.The rebels have also used conventional guerrilla tactics, both inside Chechnya and in neighbouring areas of Russia. Four times this month Russian troops have stormed buildings where militants were holed up. Russian security services link the mainly Muslim Chechen guerrillas to al Qaeda, which also uses suicide bombings. The Chechens deny any formal link.