Stuart WILLIAMS and Fulya OZERKAN - The opposing sides in Turkey's tightly-contested referendum on expanding President Recep Tayyip Erdogan's powers made a last push for votes Friday as the arrest of five suspected militants fuelled security concerns.

Opinion polls - usually treated with caution in Turkey - have predicted a tight outcome on Sunday despite the considerable advantages of the 'Yes' campaign in both airtime and campaign resources. The referendum will take place under a state of emergency that has been in place since last summer's failed coup which has seen some 47,000 arrested in the biggest crackdown in Turkey's history.

Analysts regard the referendum as a turning point in the modern history of the country that will affect not just the shape of its political system but also its relations with the West.

If the new system is passed, it will abolish the office of prime minister, enabling the president to centralise all state bureaucracy under his control and also to appoint cabinet ministers.

Supporters see the new system as an essential modernisation step for Turkey to streamline government but opponents fear it risks granting Erdogan authoritarian powers.

Erdogan has raised hackles in the West throughout the campaign with his repeated denunciations of the European Union, which Turkey has sought to join for the last half century. "April 16 will be an answer to the European Union," Erdogan said in a TV interview late on Thursday. He expressed confidence that the new presidential system would be approved, saying there were no longer undecided voters. "'Yes' has gone up considerably, while 'No' has gone down," he said.

Conflicting polls

A poll by the Konda group showed 'Yes' ahead at 51.5 percent but the Sonar group has projected a 'No' vote of 51.2 percent, and with other polling companies producing different figures the outcome remains uncertain.

Erdogan will on Friday speak in Konya, the Anatolian city seen as the heartland of conservative supporters who have benefited from his rule.

The leader of the opposition Republican People's Party (CHP) Kemal Kilicdaroglu has called for a 'No' vote, arguing there was too much uncertainty over the consequences of the new system. "We will altogether write a legend of democracy (on Sunday) because our questions have been left unanswered," he told reporters in Istanbul. The referendum is taking place after a bloody year of terror attacks in Turkey blamed on militants and Kurdish militants.

Adding to security concerns, Turkish police on Friday detained five suspected Islamic State militants in Istanbul accused of planning a "sensational" attack targeting the weekend referendum.

Turkish authorities had on Tuesday detained another 19 suspected IS supporters in the Aegean city of Izmir, accused of planning to sabotage the vote.  In the latest issue of its Al-Naba magazine, IS called for attacks on polling stations in Turkey.

Last-minute spat?

Campaigning is allowed until 6:00 pm (1500 GMT) on Saturday and voting in the country's east gets under way at 7:00 am (0400 GMT) on Sunday and an hour later elsewhere.

Meanwhile, a last-minute dispute appeared to be brewing between Erdogan's ruling Justice and Development Party (AKP) and its main political ally in implementing the plan, the Nationalist Movement Party (MHP).

An advisor to Erdogan suggested this week Turkey could form a federal system if 'Yes' won in a move that would be an anathema to the nationalists.

But MHP leader Devlet Bahceli quickly responded saying he would dismiss any advisor of his if they made similar remarks.

"Have you heard such a thing from me? No," Erdogan hit back.

In a bid to prevent any last-minute schism with the MHP, Prime Minister Binali Yildirim also said he would resign if there was any move towards a federal structure for Turkey.

UN raps Turkey

Ahead of the vote, UN experts accused Turkey of "massive violations" of the right to education and work, citing figures suggesting that since the state of emergency was declared, some 134,000 public servants had been dismissed.

The dismissals "cannot be justified by reference to Turkey's longstanding international human rights obligations," said four UN special rapporteurs in a statement.

However, Turkey's foreign ministry rejected the "political statement", adding it would diminish the value of the UN mechanisms. –AFP