(CNN) -- The death toll after suicide bombings at a Shiite mosque in southeastern Iran has climbed to at least 39 people, state media reported.
State-run Press TV reported Thursday that 83 people were wounded in Wednesday's attack at the Imam Hussein Mosque in Chabahar, Iran.
The Jundallah Sunni armed group claimed responsibility for the bombings on its website, Iran's semi-official Mehr News Agency reported.
Earlier this week, the International Campaign for Human Rights in Iran said that the region -- which borders Pakistan and Afghanistan -- has been the site of fighting between Jundullah and government security forces.
The human rights group said the Iranian government asserts that Jundullah is funded by western intelligence, but the U.S. State Department added the group to its list of terror organizations.
"We hope this grotesque act will not lead to reprisals harming other innocent civilians," said Hadi Ghaemi, a spokesman for the human rights group.
The violence comes as Shiite Muslims across the world are observing Ashura, a period of mourning commemorating the martyrdom of Imam Hussein, the Prophet Mohammed's grandson and one of Shiite Islam's holiest figures.
The governor of Chabahar said a suspect has been taken into custody.
"The main perpetrator of the terrorist attack, which has killed and wounded a number of Iranians, has been arrested," Gov. Ali Bateni told IRNA.
CNN's Mitra Mobasherat contributed to this report.