HARI SREENIVASAN, PBS NEWSHOUR WEEKEND ANCHOR: The administration of Turkey's president, Recep Tayyip Erdogan, is claiming victory in today's referendum to expand the president's executive powers. With 99 percent of the votes counted, Turkish election officials said 51 percent of Turks voted "yes" to amend the country's constitution. It will result in abolishing the office of prime minister and allowing the president to draft the budget, issue decrees, and appoint judges without parliamentary approval.

President Erdogan cast his ballot in Istanbul and called a "yes" vote, quote, "a choice for change and transformation."

Opponents charge the changes will lead to authoritarian, one- man rule, and they have already begun challenging the results.

For more on the referendum, I'm joined via Skype from Istanbul by "New York Times" reporter Patrick Kingsley.

Patrick, this is close. I'm sure you've been watching it all night. But one side is claiming victory and the other side says, not so fast.

PATRICK KINGSLEY, NEW YORK TIMES: Well, exactly. The administration of President Recep Tayyip Erdogan has claimed victory. His prime minister, Binali Yildirim, who will be out of a job, thanks to this constitutional change, has just made a speech claiming victory. The main opposition party, however, is contesting what it says around 37 percent of ballot boxes and that could be well over 2 million votes in there.

SREENIVASAN: What are the concerns that the opposition has?

KINGSLEY: They're claiming that that there had been ballot stuffing. There had been circulating unverified vides of individuals taking, for example, five ballot slips and placing them within a ballot box. And the main opposition party, the CHP, says there could be thousands of such instances, but this is yet to be proved.

SREENIVASAN: How strong is the possibility that the opposition can mount enough of a challenge to take over the rule of president in a couple of years? I mean, it's — for people watching in the United States, how competitive is it there?

KINGSLEY: It feels very unlikely at the moment. President Erdogan is without doubt the most popular man in Turkey, even if he is a very divisive man and it seems to split the country in two. There is another figure within the main opposition party who is currently out of jail who could mount a particularly strong opposition to him, never say never, but he seems unlikely to win in 2019 and his political party seems likely to be the biggest party in parliament.

The only means of writing a check on the president's power would be if opposition party has managed to form a majority in parliament. But the way that the political landscape in Turkey looks right now, that also seems unlikely.

SREENIVASAN: How much of a factor did the attempted coup play into this vote?

KINGSLEY: I think it may have a major effect, because President Erdogan was able to show that there was a very real threat to Turkish democracy. He was able to say, we were elected and the faction within the army tried to surface from power. And for that reason, we need to create stability and you the electorate need to vote for this constitutional change that would centralize power in the hands of the president.

SREENIVASAN: Was Turkey and was Erdogan conscious of what the rest of the world thought about this referendum and what happens tomorrow?

KINGSLEY: They were very conscious because and the reason why President Erdogan and his allies stoked so many battles in particular with European and European politicians, he called the Europeans Nazis, in particular in Holland and Germany, the reason why he did all that was to create the illusion of a Turkey under siege, and had the effect of rallying nationalist voters to his cause. It made them to think that President Erdogan was the only person standing up for them and Turkey. And for that reason, they needed to vote for him. So, he was very aware of what people thought of Turkey and he would play on that and use that to his advantage.

SREENIVASAN: All right. "New York Times" reporter, Patrick Kingsley, joining us via Skype from Istanbul tonight — thanks so much.

KINGSLEY: Thank you.