Turkish nationalist opposition leader signals won't support presidential system

ANKARA (Reuters) - The head of Turkey's nationalist opposition said on Tuesday efforts by the ruling AK Party to introduce an executive presidency were "invalid," ruling out speculation he could back a new constitution to change the country's political system. Speaking to his group in parliament, Nationalist Movement Party (MHP) Chairman Devlet Bahceli also said creating an atmosphere for snap elections following an announcement by Prime Minister Ahmet Davutoglu last week that he would resign amounts to "treason." Bahceli has blocked efforts to challenge his position after his party saw its share of support fall by more than 25 percent between June and November elections. Opinion surveys show a change in the MHP's leadership could double its vote. (Reporting by Ercan Gurses; Writing by Ayla Jean Yackley; Editing by Daren Butler)