Thousands of protesters took to the street in a rally against the controversial victory, which will give President Erdogan sweeping new powers and could see him remain as president until 2029.
It comes as shocking video from last night's demonstrations appeared to show a protester being attacked by pro-Erdogan Turks. In the clip, a person is chased down by a large group, who surround them and kick them to the ground.
This morning, opposition parties complained of a number of irregularities in the voting, and were particularly incensed by an electoral board decision announced on Sunday afternoon to accept as valid ballots that did not bear the official stamp.
'The Supreme Electoral Board changed rules mid-game, after the ballot envelopes were opened, in a way contrary to laws,' said Kemal Kilicdaroglu, head of the main opposition People's Republican Party.
Earlier, the party's vice chairman, Erdal Aksunger, said it would challenge between 37 per cent and 60 per cent of the ballot boxes and accused the state-run Anadolu Agency's election result figures of being inaccurate.
But electoral board head Sadi Guven defended the decision. 'There is no question of changing the rules in the middle of the game,' he said.
On Monday he explained the decision, saying he did not want people who had been given unstamped ballots by mistake to be 'victimised'.
Guven also denied that any of the ballot papers cast without a stamp had been fraudulent or fake.
Speaking to his supporters yesterday, Erdogan said: 'There are those who are belittling the result. They shouldn't try, it will be in vain. It's too late now.'
Last night protesters raided their kitchen cupboards and banged pots and pans as a symbol of defiance against the result.
51.3 per cent voted for giving Erdogan more power, compared to 48.7 per cent for the 'no' vote, according to state agency Anadolou.