BANGKOK — A deadly cathedral bombing in the Philippines in January was a suicide attack carried out by an Indonesian couple who once tried to reach Islamic State territory and were deported from Turkey, the Indonesian police said on Tuesday.

The married couple, identified as Rullie Rian Zeke and Ulfah Handayani Saleh, went to Turkey in 2016 with hopes of crossing the border into Syria, the police said. Instead, they were arrested in January 2017 and sent back to Indonesia.

The bombing, consisting of two detonations, struck the Cathedral of Our Lady of Mount Carmel on the southern island of Jolo, where the government has long fought Muslim insurgents. At least 23 people were killed and more than 100 wounded in the assault, which took place just as worshipers gathered for Mass. Through various online bulletins, the Islamic State claimed responsibility.

Terrorism officials and independent experts have warned that Indonesia and other Southeast Asian nations face a serious threat from hundreds of returnees who traveled to Syria and Iraq to join the Islamic State. The attack in January showed that they must also be wary of those who were deported from other countries before they could reach their destination.