A hand grenade has exploded in the courtyard of a Roman Catholic church in Gaza City, but there were no reported casualties or damage, a parish official said.

An investigation was opened into the attack, which occurred Wednesday night at the city's southern Zeitun district, Hamas police spokesman Ayoub abu Shaar told the Associated Press news agency on Thursday.

"In the middle of the night, unknown assailants threw a hand grenade at the church. It landed in the courtyard and exploded but caused no damage or casualties," another source, requesting anonymity, told Agence France Presse news agency.

"We won't let this juvenile and irresponsible act affect us and will carry on our work as normal," he added, without saying who might have been responsible.

'Abusive slogan'

A Gaza-based rights group, the Palestinian Centre for Human Rights, condemned the act and called for a "serious investigation into this crime".

The group told the Associated Press news agency that an "abusive slogan" was written on the church wall.

According to the Latin Patriarchate of Jerusalem, there are only some 1,500 to 3,000 Christians among the 1.5 to 1.7 million, predominantly Muslims living in the Gaza Strip.

The enclave has seen several attacks against Christian targets in the past few years.

In 2011, a bomb targeted the director of Gaza's Anglican hospital, who escaped unharmed.

A library belonging to the Baptist church was damaged in a bomb attack in 2007.