The Christian governor of Jakarta has been sentenced to two years in prison by an Indonesian court that found him guilty of blasphemy.

The charge related to a reference by Basuki Tjahaja Purnama – better known by his nickname Ahok – to a Quranic verse in his re-election campaign last September. His opponents had used the verse to argue that Muslims should not be led by non-Muslims; Ahok said they had used it to trick people into voting against him.

An edited version of his speech was posted online and went viral, sparking mass demonstrations against him including one that drew around half a million protesters.

One judge, Dwiarso Budi Santiarto, told the court after passing the unexpectedly harsh sentence: 'As part of a religious society, the defendant should be careful to not use words with negative connotations regarding the symbols of religions, including the religion of the defendant himself.'

Another judge, Abdul Rosyad, said the jail sentence was because Ahok had 'caused anxiety and hurt Muslims' and had felt no guilt.

Ahok, who will appeal his sentence, lost the election last month to a Muslim rival and will hand over his office in October.

As a Christian and ethnic Chinese, he is doubly disadvantaged in Indonesia's predominantly Muslim society, in which Christians are increasingly under pressure. Despite the political motivation many observers see in his trial, the case is regarded as worrying by rights activists.

Andreas Harsono, an Indonesia researcher at Human Rights Watch, told the Guardian the verdict was 'a sad day for Indonesia'.

'Ahok's is the biggest blasphemy case in the history of Indonesia,' he said. 'He is the governor of Indonesia's largest city, an ally of the president. If he can be sent to jail, what could happen to others?'

Harsono said more than 100 Indonesians have been convicted of blasphemy in the past decade and acquittals were extremely rare.