President Recep Tayyip Erdoğan said his ruling Justice and Development Party (AK Party) could seek to form a coalition if it fails to secure a parliamentary majority in Sunday's elections, but said the prospect of this is "very, very low".

Polls indicate the elections may be closer than anticipated when he called the snap elections in April, suggesting he may be pushed to a second-round run-off for the presidency, and his AK Party could lose its majority in the 600-seat assembly.

"If it is under 300 (seats), then there could be a search for a coalition," Erdoğan said in an interview with the Kral FM radio station late on Wednesday.

He added that the probability of this was "very, very low".

However, Erdoğan did not indicate with which party he could form a coalition or how difficult the task could be.

The Turkish lira, which has slumped more than 20 percent against the dollar this year, has extended losses over the last week on concern about the prospect of political uncertainty following the elections.

Investors fear political deadlock if the AK Party loses its majority in parliament as it would put a brake on Erdoğan's ability to exercise the powers of the new presidential system.

The conservative AK Party formed the People's Alliance with the Nationalist Movement Party (MHP) before the elections, which will herald a switch to a new powerful executive presidency narrowly approved in a referendum last year.

Opposition parties, the center-left secularist CHP, the right-wing Good Party (IYI Party - IP) and the Islamist-conservative Felicity Party (SP) also formed the Nation Alliance, which excluded the pro-PKK Peoples' Democratic Party (HDP). If the HDP exceeds the 10 percent threshold of votes needed to enter parliament, it will be harder for the AK Party to achieve a majority.

Speaking late Wednesday in an interview with broadcaster Fox, main opposition Republican People's Party (CHP) Chairman Kemal Kılıçdaroğlu said that Erdoğan's comments shows the inability of the two parties of the People's Alliance.

"Let's take a look how they begin; why did they change the constitution and came before the nation? They said 'Turkey suffered a lot from coalition governments, the country cannot be governed by coalitions, which is why we are changing the regime.' The point we have arrived at is that Turkey cannot be ruled without a coalition, that a party cannot rule without 51 percent," Kılıçdaroğlu said, adding that coalitions cannot be formed in Parliament with the new system and only one party will likely be included in the presidential cabinet.

Opposition parties objected to the changes narrowly accepted in the April 16, 2017 referendum with 51.4 percent of the votes and vow to return to the parliamentary system.

Under the constitutional changes going into effect after the elections, the number of lawmakers in parliament will increase to 600 from 550 currently.

The AK Party has held a majority in parliament for nearly all its 15 years in power, only losing it in the June 2015 election. After parties failed to form a coalition then, Erdoğan called a fresh election in November which restored the AK Party majority.

MHP leader Devlet Bahçeli said on Monday another election could be held if his alliance with the AK Party cannot form a majority in parliament after Sunday's vote.