Turkey's Prime Minister Binali Yildirim declared victory in the referendum bid to convert Turkey from a parliamentary to a strong president system of government.

The historic referendum, which passed by a narrow margin, grants more power to President Recep Tayyip Erdogan, who promised when he was elected in 2014 to be a "different kind of president."

But even as Erdogan's supporters set off fireworks to celebrate their victory, Turkey's main opposition party said they will challenge many of the votes.

Erdogan said he hopes the referendum results would benefit Turkey, and that the nation made a "historic decision," in an address after Yildirim's declaration.

The vote has divided Turkey, with supporters claiming the change will bring stability and efficiency to the government, while opponents have said that the move is a dangerous step toward one-man rule. Under the changes, President Erdogan could stay in power through 2029.

As NPR's Peter Kenyon reported in a preview, "the vote comes at a perilous time."

"Turkey remains under a state of emergency declared last July, following a failed coup that left nearly 300 people dead. The Erdogan government has used the emergency powers to conduct a sweeping purge of the military, judiciary and civil service. More than 100,000 people have been fired or arrested, including more than 100 journalists."

The opposition to the referendum said it's been difficult to run an effective campaign in this environment of fear and sweeping arrests. The AP reports that supporters of the "yes" vote have dominated the airwaves, while supporters of the "no" vote have complained of intimidation.

Under the new system, power will be concentrated under the president, who was previously head of state, but not head of government. President Erdogan has taken a more active role than his predecessors, but until the referendum the Prime Minister remained the chief executive.

The new system will no longer require the president to be nonpartisan, so Erdogan can rejoin the party he co-founded, and have increased influence over who runs for Parliament. Critics say there's also a loophole in the new laws that could allow Erdogan to run for a third term. The prime minister role will also be done away with after the next election in 2019.

NPR's Peter Kenyon has reported that there is one change pro-democracy groups are applauding though — the end of military courts.

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