The Turkish government on Tuesday stood behind a top cleric who has been accused of making offensive comments about the republic's founder Mustafa Kemal Ataturk during a sermon at Istanbul's iconic Hagia Sophia.

While leading Friday prayers at the building, reconverted this month to a mosque, Ali Erbas, head of the top religious body known as Diyanet, invoked the name and charter of Ottoman Sultan Mehmet II, who led the conquest of Constantinople in 1453.

Erbas said Mehmet endowed Hagia Sophia to believers on condition that it should remain a mosque for all time. "Any property that is endowed is inviolable in our belief and burns whoever touches it," he said. "The charter of the endower is indispensable and whoever infringes upon it is cursed."

That comment ignited a debate with opposition parties arguing that the sermon was a clear insult to Ataturk who turned the mosque into a museum. "It is out of the question for (Erbas) to defame Ataturk," presidential spokesman Ibrahim Kalin told private television channel CNN-Turk.  "We never accept any attack on Ataturk," he said, adding that starting such a debate lacked goodwill and was part of an attempt to create an "artificial agenda".

The right-wing Iyi (Good) Party lodged a complaint against Erbas on Monday, while Ozgur Ozel of the main opposition Republic People's Party (CHP) vowed Erbas would "pay the price of damning Ataturk".

The sixth-century Byzantine era edifice was built as a cathedral but turned into mosque after the conquest of Constantinople in 1453. The new republic founded by Ataturk adopted a decree in 1934 making it a museum.

This month, a top Turkey court annulled that decree and reconverted Hagia Sophia into a mosque, which opened to first Muslim prayers last Friday.