The chief agitator behind last year's child suicide bombings in Indonesia's second-biggest city, Surabaya, has been sentenced to 10 years in prison.

Key points: Umar held Jamaah Ansharud Daulah meetings in East Java

Umar held Jamaah Ansharud Daulah meetings in East Java Prosecutors said Umar's sermons urged followers to prepare for attacks against Indonesian police

Prosecutors said Umar's sermons urged followers to prepare for attacks against Indonesian police Among his recruits was Dita Oepriarto, the mastermind of the Surabaya bombings in May 2018

Abu Umar, also known as Syamsul Arifin, was the East Java provincial leader of the terrorist group Jamaah Ansharud Daulah (JAD) and held regular motivational meetings attended by some of Indonesia's most extreme militants.

Prosecutors, who recommended a 15-year jail sentence, said the defendant was responsible for mass casualties through his teachings for JAD.

Among those he recruited was Dita Oepriarto, the mastermind of the Surabaya bombings, who led his wife and children — one of them just nine years old — to commit suicide attacks against churches during Sunday mass in May 2018.

The day after the church bombings, Tri Murtiono and his family, riding two motorbikes, bombed the Surabaya police headquarters.

Their youngest daughter, just eight years old, was the only member of the family to survive.

In all, 28 people were killed and around 50 were wounded.

Surabaya's police headquarters was attacked a day after bombings at three churches. ( AP: Achmad Ibrahim )

During the trial, Abu Umar denied knowledge of the Surabaya plot, claiming Dita Oepriarto acted alone in the planning and execution of the attacks.

However, according to a report by the Institute for Policy Analysis of Conflict (IPAC), Umar was a keynote speaker at a number of meetings throughout 2017, where he urged his followers to prepare for "total war" by bombing churches and government offices, especially those of the police.

At one of the meetings in early January 2017, Abu Umar addressed local leaders of JAD, including both Dita Oepriarto and Tri Murtiono, along with their wives and children.

The court heard Umar's sermon praised martyrdom, encouraged obedience to the caliphate declared by the Islamic State group in Syria and Iraq, and urged his followers to prepare for attacks against Indonesian police and military targets.

He was also accused of planning an attack on police with a Beretta pistol, which he had kept buried in the backyard of an associate's home.

Prosecutors claim in March 2018, he took the gun to the city of Malang with two other members of JAD, but they cancelled the attack because the street was too crowded with traffic.

During the trial, Umar resigned from JAD, apparently to avoid responsibility for crimes committed by the banned group in the future.

Last June, the founder and spiritual leader of JAD, Aman Abdurrahman, was sentenced to death over his role in a string of deadly bombings.

Abdurrahman was one of the first people to support the caliphate declared by the Islamic State group in 2014, but during his trial he condemned the Surabaya bombings, saying they were carried out by crazy, desperate people, against the values of Islam.