MOSCOW (Reuters) - Chechen security forces killed up to 20 rebels in a helicopter attack near the capital Grozny, the regions leader Ramzan Kadyrov said on Friday. Kadyrov, whose region has suffered a sharp rise in attacks blamed on the rebels this year, said he believed one of those killed might be Doku Umarov, who had declared himself the head of a North Caucasus 'emirate. We cannot confirm he has been killed until an autopsy is carried out on the fragmented bodies of the militants, Kadyrov said in comments posted on the government website (chechnya.gov.ru) . Russian President Dmitry Medvedev said on Thursday an upsurge of violence in the North Caucasus region, which includes Chechnya, Dagestan and Ingushetia, was Russias biggest domestic problem. The patchwork of republics along Russias southern flank has seen a wave of attacks in recent months that local leaders say are fuelled by a potent mixture of clan feuds, poverty and heavy-handed tactics by law enforcement agencies. Special forces troops launched a ground operation on Friday after helicopter gunships opened fire on the suspected rebels, Kadyrov was quoted as saying by Interfax news agency. He said government forces suffered no casualties. The battle took place in a mountain area outside the village of Shalazh, 30 kms southwest of Grozny, the Chechen government statement said. It was not immediately possible to confirm the governments account of the battle.