KABUL, Feb 22 (Reuters) - Afghan President Hamid Karzai appealed to his countrymen for calm on Wednesday and urged them to stop the violence that killed at least six people in two days of nationwide protests over the burning of Korans at the country's biggest NATO base.

"Afghan security forces should not use violence during the protests and protect civilian lives and property," Karzai said in a statement, adding he was deeply saddened by the loss of civilian lives. Afghan authorities have ordered an investigation to see if Afghan police or foreigners took aim at the crowds.

"Protests are the right of the people but I ask my countrymen to avoid violence," he added of the protests, which drew thousands of angry Afghans to the streets.

(Reporting by Hamid Shalizi, writing by Amie Ferris-Rotman, editing by Rob Taylor)