A Roman Catholic priest has been shot dead inside a chapel in the northern Philippines as he was preparing to say Mass, the third cleric to be killed in six months, police say.

Father Richmond Nilo was behind the altar of the Nuestra Senora de la Nieve Chapel in Zaragoza town in Nueva Ecija province, 96 kilometres north of Manila, when he was shot dead on June 10 evening.

Two unidentified gunmen shot the priest through a window four times, according to an initial police investigation.

The attack occurred less than a week after a priest was wounded in a shooting in the city of Calamba in Laguna province, south of Manila, on Wednesday.

Nilo was the third Catholic priest to have been killed in the Philippines since December 2017, according to the Catholic Bishops Conference of the Philippines (CBCP).

“I am deeply sad and bothered because we may note that Father Nilo is the third priest to be killed in these recent months,” CBCP President Archbishop Romulo Valles said.

On April 29, Father Mark Ventura, 37, known for his anti-mining advocacy, was shot dead after celebrating mass in the northern province of Cagayan.

On December 4, 72-year-old Father Marcelito Paez was shot dead in Jaen town in Nueva Ecija province after facilitating the release of a political prisoner and dropping the former detainee off at his home.

National police chief Oscar Albayalde condemned the killings, but stressed that the cases were not related to each other and did not represent a pattern of attacks against Catholic priests in the Philippines. He urged Catholic priests who have received threats to seek police protection