Turkey's governing AK Party is to hold an extraordinary congress in the coming weeks, amid speculation over the future of PM Ahmet Davutoglu, media say.
Reports suggest the congress will elect a new leader and that Mr Davutoglu, who met President Recep Tayyip Erdogan on Wednesday, will not stand again.
The apparent rift has surfaced after long-rumoured tensions between the two.
Mr Erdogan hand-picked Mr Davutoglu to succeed him as head of the AK Party after the former was elected president.
But Mr Davutoglu was reportedly uneasy about Mr Erdogan's desire to change Turkey's political system to a presidential one, shifting the balance of power away from the prime minister.
In a sign of Mr Davutoglu's weakening influence, he was stripped last week of the authority to appoint provincial AK Party officials.
Turkish media reported that Mr Davutoglu would hold a news conference on Thursday following a gathering of the party's central executive committee.
The development comes at a time of increasing instability for Turkey, which is tackling an escalating conflict with the rebels of the Kurdistan Workers' Party (PKK), terror attacks by the so-called Islamic State, and an influx of migrants and refugees.
Turkey is also in the midst of implementing a key deal with the European Union, brokered by Mr Davutoglu, to limit the number of refugees flowing across its border in return for accelerated EU accession talks and financial aid.
The future of that agreement, which Mr Davutoglu was seen as having agreed with little input from the president, could be plunged into doubt by his departure.
A party official told Reuters the congress could be held as soon as 21 May and would begin no later than 6 June, the first day of the Islamic holy month of Ramadan.
Among those tipped as successors to Mr Davutoglu are Transport Minister Binali Yildirim, who is close to Mr Erdogan, and Energy Minister Berat Albayrak, who is the president's son in law.
Analysis: Mark Lowen, Turkey Correspondent
Recep Tayyip Erdogan is arguably the most formidable politician since modern Turkey's founding father Ataturk.
After 11 years as prime minister, he was elected president in 2014 - but under a parliamentary system, in which his role should be largely ceremonial.
The fiercely ambitious Mr Erdogan is intent on changing that to a presidential system, which he says would make Turkey function more effectively, but which would also significantly increase his powers.
As president, he chose a prime minister who he thought would be pliant: the ex-foreign minister and bookish former academic, Ahmet Davutoglu.
But it seems he miscalculated. Seeing wavering public support for a presidential system, realising that he would be significantly sidelined should it materialise and disagreeing with Mr Erdogan on a growing list of policies, the prime minister has quietly dissented.
There has been little public show of disobedience, no clear spat. That's not Mr Davutoglu's style. Nor is it likely, given the widespread fear of Mr Erdogan within the ruling AKP.
But little by little, the signs have grown.