Video caption Soldiers were deployed to the area after the explosions

Two bombs at a Roman Catholic cathedral in southern Philippines have killed 20 people and injured dozens more, local officials say.

The Islamic State (IS) group said it was behind the attack on Jolo island, where jihadist groups are active.

The first blast happened as Sunday Mass was being celebrated. A second device exploded outside as soldiers responded.

The attack came days after a majority-Muslim area in the region voted for greater autonomy in a referendum.

A statement from IS said the attack was carried out by "two knights of martyrdom" against a "crusader temple".

Jolo has long been a base for militants, including those of the Abu Sayyaf group. Several of its factions have declared allegiance to IS.

What is known about the attack?

The local officials say the first blast happened at 08:45 local time (00:45 GMT) inside the Cathedral of Our Lady of Mount Carmel, which has been hit by bombs in the past.

The second explosion was shortly afterwards on the doorstep of the church.

Police initially put the death toll at 27 but later lowered it to 20, saying there was double counting in earlier official reports.

Most of the victims are civilians.

Image copyright Huw Evans picture agency Image caption The bomb attack devastated the church in Jolo

Images posted on social media showed the main road leading to the church sealed off by soldiers in armoured personnel carriers.

Some of the wounded were evacuated by air to the nearby city of Zamboanga.

Calling the attack a "dastardly act", Defence Secretary Delfin Lorenzana urged the local population to work with the authorities to "deny terrorism any victory".

"We will use the full force of the law to bring to justice the perpetrators behind this incident."

Image copyright EPA Image caption The army has been deployed to the area after the bomb blasts

In last week's referendum, voters approved the creation of the Bangsamoro Autonomous Region in majority-Muslim areas of southern Philippines.

But voters in Sulu province, where Jolo is located, rejected it.

The referendum was the result of a peace deal between the government and the Moro Islamic Liberation Front (MILF).

The authorities have previously expressed hopes that the vote could be a political solution to try to end decades of fighting between Islamist separatists and the Philippine army in the predominantly Catholic country.

More than 120,000 people have died in the violence.