* Security situation has worsened since, Telenor CEO says * Activists say sale leaves them vulnerable * M1 Group not available for comment * tmsnrt.rs/3hoGpIL (Adds quotes from Telenor CEO, activists, investor, analyst, share, bullet points, graphic) OSLO, July 8 (Reuters) - Norwegian telecoms firm Telenor has sold its Myanmar business, blaming the difficulties of operating under the military junta and dealing a blow to activists who say they relied on the only Western operator for communications. Telenor, one of the biggest foreign investors in Myanmar, sold its Myanmar operations to Lebanese investment firm M1 Group for $105 million, announcing its retreat from a country that slid into chaos after a military coup in February.