Turkey said on Friday its top four military chiefs were all seeking retirement, in moves that appeared to reflect a deep rift between the secularist military and conservative government.
The reason for the generals' move was not immediately clear, but tensions between the military and the government of Prime Minister Tayyip Erdoğan have run high in recent years.
The Supreme Military Council is due to hold a major twice-yearly meeting next week dealing with key appointments and President Abdullah Gül and Erdoğan met Koşaner on Friday to discuss the matter.
Following the announcement Erdoğan met the head of Turkey's gendarmerie paramilitary force, General Necdet Özel, and they subsequently went separately to the presidential palace to meet President Abdullah Gül, fuelling speculation Özel may be appointed to replace Koşaner.
By tradition, the head of the ground forces replaces the armed forces chief when he retires.
Friction between the government and military, traditionally guardians of the secular state, has been fueled by the continuing trial of 200 military officers accused of plotting to overthrow the government.
The "Sledgehammer" case, arising from an alleged coup plan presented at an army seminar in 2003, is one of several setting Turkey's secularist establishment against Erdoğan's ruling AK party.
Some 165 military personnel, including more than 40 generals, are in custody in the coup plot trials, severely damaging the military's operational ability.
The Turkish lira weakened sharply on the news to 1.6964 against the dollar from an interbank close of 1.6805 on Friday.
