Authorities in the Philippines say they have arrested at least eight suspected militants accused of having links with past attacks in the country's south.
One of those detained was Ahmad Santos, the head of a group of Islamic converts called the Rajah Solaiman Movement.
A military spokesman said the suspects were arrested in pre-dawn raids in the southern city of Zamboanga.
He alleged that they had been planning bomb attacks in predominantly Christian cities around the Philippines.
Weapons, explosives and maps of the capital, Manila, were reportedly seized during the raid.
According to police intelligence officials, the Rajah Solaiman group is believed to have forged an alliance with two al-Qaeda-linked organisations - Philippine-based Abu Sayyaf and the regional militant group Jemaah Islamiah (JI).
Converts to Islam
"This is definitely a big catch," said Lt Gen Edilberto Adan, commander of the army's Southern Command.
Ahmad Santos - also known as Hilarion del Rosario - is believed to have founded the Rajah Solaiman Movement in the late 1990s, after he converted to Islam.
He is then thought to have received bomb training from members of JI on the island of Mindanao.
Members of the Rajah Solaiman group are also suspected to have been involved in the sinking of a ferry near Manila in 2004 - an attack that killed more than 100 people.
Abu Sayyaf has claimed responsibility for that attack, but one of the self-confessed bombers was a Muslim convert from the Rajah Solaiman Movement.
According to security officials, converts are often used to carry out attacks in the Philippines because they can easily blend in with the majority Christian population.
The authorities are concerned that the emergence of convert groups such as the Rajah Solaiman Movement could expand the reach and strength of Abu Sayyaf and JI.