A Murdoch University terrorism expert has warned that Indonesia should brace itself for more attacks in the wake of a series of shocking suicide bombings committed by families in the city of Surabaya in East Java.

Dr Ian Wilson, a politics and security studies lecturer from the Asia Research Centre, said the timing of the attacks – just before the start of Ramadan on 15 May – may not be coincidental.

“We’ve seen a pretty significant increase in activity over just the past couple of weeks in Indonesia, so it’s reasonable to assume there are likely more attacks being planned,” he said in The Diplomat.

A family of six, including a girl aged nine, targeted three churches at the weekend, killing at least 13 and injuring more than 40 churchgoers. On Monday, the police headquarters in Surabaya were also attacked by suicide bomber parents who intentionally involved their children in the deadly violence. Attacks of this kind are unprecedented.

Dr Wilson said an increase in attacks during Ramadan has been a trend elsewhere in the world, linked to the 2015 call by Islamic State to “commemorate” the holy month of fasting with violence and bloodshed.

In another interview on ABC’s The Drum, Dr Wilson said it appeared that the family who carried out the church bombings “slipped through the net” of Indonesia’s intelligence community and the attacks could result in a rushing through of draft revisions to existing anti-terrorism legislation.

“It’s believed they could be among roughly 500 Indonesians who traveled to Syria to join Islamic State or to live in IS controlled territory, and are now returning radicalised as IS’s power fractures in the region,” he said.

“The family involved in the church attacks is believed to have returned before de-radicalisation and reintroduction programs run by civil society organisations in Indonesia, were operating.

“There is a broader backdrop to this where there’s been a stalling in parliament of revisions to anti-terror legislation. And one aspect of this legislation that is yet to be ratified is criminalising involvement in fighting in a foreign country.

“This has meant that the primary means through which those returning from foreign conflicts have been managed has been through ad hoc social rehabilitation programs.

“The bombings could generate an imperative for the government to tighten up the programs that are in place and more closely track the people returning from Syria and Marawi in the southern Philippines, which has seen a concentration of militants from the region.”

Dr Wilson said he believed the spate of attacks were due in part to problems of intelligence operations and policy frameworks rather than increasing radicalisation in Indonesian society more generally.

“It’s important to separate out the politicisation of identity,” he said. “We saw this last year around the elections in Jakarta where the incumbent Christian Chinese governor Ahok was pursued through a sectarian campaign. But with the recent bombings we are talking about a distinct phenomena to that even though some might say it’s an enabling environment for some of the more radical groups.”

You can watch Dr Wilson’s full interview on The Drum here.