ISTANBUL — Turkey's Tayyip Erdogan emerged victorious on Monday from his biggest electoral challenge in a decade and a half, giving him the sweeping, executive powers he has long sought and extending his grip on the nation of 81 million until at least 2023.

The most popular — yet divisive — leader in modern Turkish history, Erdogan pledged there would be no retreat from his drive to transform Turkey, a deeply polarized nation that is both a NATO member and, at least nominally, a candidate to join the European Union.

Erdogan, 64, is loved by millions of devoutly Muslim working class Turks for delivering years of stellar economic growth and overseeing the construction of roads, bridges, hospitals and schools.

The president and his ruling Islamist-rooted AK Party claimed victory in Sunday's presidential and parliamentary polls after defeating a revitalized opposition that in recent weeks had gained considerable momentum and looked capable of staging an upset.

"It is out of the question for us to turn back from where we've brought our country in terms of democracy and the economy," Erdogan told jubilant, flag-waving supporters on Sunday night.

Critics say campaigning took place under deeply unfair conditions, with Erdogan dominating media coverage in the run-up to the vote, and his opponents getting little air time. One rival presidential candidate, the head of a pro-Kurdish party, campaigned from a prison cell, where he is detained on terrorism charges he denies. He faces 142 years in prison if convicted.

The High Election Board (YSK) said on Monday the elections had been "healthy".

Erdogan took 52.5 percent of the vote in the presidential race, with more than 99 percent of the votes counted. His AK Party took 42.5 percent in the parliamentary polls, and was boosted by its nationalist allies, which outstripped expectations and took 11.1 percent.

Voter turnout was high, at nearly 87 percent.

The vote ushers in the powerful executive presidency backed by a narrow majority in a 2017 referendum.

Critics, including rights groups, have said this will further erode democracy and entrench one-man rule. They point to a widening crackdown since a failed 2016 military coup that has seen some 160,000 people detained and media outlets shut down.

Under the new system, the office of prime minister will be abolished. The president will be able to issues decrees to form, regulate ministries and remove civil servants, all without parliamentary approval.

The lira currency, which has lost some 20 percent of its value this year, rallied some 2 percent in early trade, while stocks rose more than 1 percent, after an eary surge, as investors bet that the result would lead to political stability - a positive for financial markets.

Although investors have been nervous about Erdogan's tightening grip on power, there had been concern that the outcome of the election could lead to policy uncertainty.

The state-run Anadolu news agency said that, based on unofficial results, the AK Party and its MHP alliance will hold 343 seats in Turkey's 600-seat parliament, with 293 of those for the AKP and 50 for the nationalists.

The main opposition Republican People's Party (CHP) will have 146 seats, the pro-Kurdish HDP 67 and the breakaway nationalist Iyi Party 44.

The opposition had said late on Sunday it was still too early to concede defeat. The main opposition's presidential candidate, the combative former teacher and veteran CHP lawmaker Muharrem Ince, took nearly 31 percent.

Ince's silence in the aftermath of the vote brought him widespread criticism from supporters on social media.

Ince was due to speak at a news conference at 0900 GMT.

Erdogan has repeatedly cast his opponents as enemies of democracy, tapping into the groundswell of nationalist feeling that followed a failed coup in 2016.

"There is no stopping for us until we bring Turkey, which we saved from plotters, coupists and political and economic hitmen, street gangs and terrorist organizations, to among the top 10 economies in the world," he said.

Expanded powers of Turkish president

The winner of Sunday's presidential election will be the first Turkish head of state to govern with expanded powers after constitutional changes were approved in April 2017.

The new 18-article constitution comes into force after presidential and parliamentary polls, transforming the parliamentary system into an executive presidency.

The current constitution was adopted in 1982 after the 1980 military coup. But critics say the changes, which were championed by President Recep Tayyip Erdogan, pave the way to one-man rule.

What changes after the implementation of the new presidential system?

Boosted powers

Under the new constitution, the president has strengthened executive powers to directly appoint top public officials including ministers.

The president can also assign one or several vice presidents. The office and position of prime minister, currently held by Binali Yildirim, would be scrapped.

The president and parliament will together also be able to choose four members of the Supreme Board of Judges and Prosecutors (HSYK), a key judicial council that appoints and removes personnel in the judiciary.

Parliament can choose seven members on its own in what will be renamed the Board of Judges and Prosecutors (HSK).

Military courts, which have convicted officers and even sentenced former prime minister Adnan Menderes to death following the 1960 coup, will in the future not be allowed.

Longer state of emergency

Under the proposed constitution, a state of emergency will be imposed in the event of an "uprising against the homeland" or "acts of violence which put the nation in... danger of being divided".

The president will decide whether or not to impose a state of emergency and then present it to the parliament.

Initially, the emergency would last six months -- as opposed to three now -- then it can be extended by parliament after a presidential request for four months each time.

Turkey has extended the current state of emergency, imposed after the failed July 15 coup, seven times.

Parliament

The number of members of the Turkish parliament rises from 550 to 600. The minimum age for MPs has also been lowered from 25 to 18.

Legislative elections will take place once every five years -- instead of four -- from now on, and on the same day as elections for the president.

The parliament will still have power to enact, modify and remove legislation. If the president were accused or suspected of a crime, then parliament could request an investigation, after obtaining a three-fifths majority of the assembly members.

The president under the new rules will not be able to issue decrees on subjects already clearly regulated by law.

Erdogan in power to 2028?

The president, who can now be a member of a political party under the changes, has a five-year term with a maximum of two mandates.

After the changes were approved last year, Erdogan returned to the ruling Justice and Development Party (AKP) he co-founded in 2001 as chairman.

Erdogan, 64, was elected president in August 2014 after over a decade as prime minister, in the first ever direct elections for a Turkish head of state.

But with the clock wound back under the new system, the changes would mean that Erdogan could stay in power for another two terms until 2028. — Agencies