Turkey's prime minister has said he has exhausted all options to form a coalition government after talks with the nationalist MHP failed, pushing the country closer to fresh elections.
Ahmet Davutoglu handed the mandate back to the president on Tuesday evening.
The main opposition CHP says it should now be given the chance to form a new government.
The political uncertainty comes amid rising violence in Turkey and neighbouring Iraq and Syria.
If no government is formed by Sunday, President Recep Tayyip Erdogan must dissolve the caretaker cabinet and arrange an interim government ahead of a new election.
Mr Davutoglu's AK Party lost its 12-year majority rule in Turkey in elections in June largely because of the success of the pro-Kurdish HDP.
The AKP's coalition talks with the CHP failed last week.
Although Mr Davutoglu's AKP secured 41% in the 7 June election, it had to seek support from a rival party to form a coalition, but failed to find agreement with the CHP on foreign policy and education matters.
Correspondents say the CHP is unlikely to secure the support it needs from both the MHP and the HDP to form a coalition of its own, making fresh elections in November a more likely outcome.
Meanwhile HDP leader Selahattin Demirtas has reportedly called for a referendum, as part of any new vote on Mr Erdogan's ambitions to bolster the powers of the Turkish presidency.
The AKP's reduced share of the vote in June appeared to have scuppered Mr Erdogan's plan to turn the country into a presidential republic, but it is likely to become an issue again in any new election campaign.
President Erdogan, for many years Turkey's AKP prime minister, has accused the HDP of being the Kurdish rebels' political wing.
Turkey's uneasy two-year ceasefire with the PKK fell apart last month, after a suicide bomb blamed on IS killed 32 young activists in the largely Kurdish city of Suruc, close to the Syrian border.
In recent weeks Turkish forces have carried out attacks on militants from the Islamic State (IS) group in Syria and have bombed Kurdish PKK camps mainly in northern Iraq.