Australians holidaying in Indonesia have been warned of the heightened risk of terrorist attacks after a spate of suicide bombings ripped through churches and a police headquarters in the country's second-largest city.
Surabaya is reeling after a car bomb exploded at a police headquarters on Monday, after a family of six blew themselves up on Sunday, killing 13 and wounding 40 Christians attending services at three churches.
The Muslim fasting month of Ramadan kicks off on Tuesday, and the Department of Foreign Affairs and Trade's travel advice urges people to exercise a high degree of caution amid an increasing threat of further attacks.
The Australian government has expressed its condolences to the victims and their families.
Home Affairs Minister Peter Dutton says Australia stands united with Indonesia.
"This threat is not going away and Australia stands absolutely united with a very, very crucial friend in Indonesia to make sure we can work with the President and... the Indonesian government to keep their people safe," Mr Dutton told reporters in Canberra on Monday.
"Evil has prevailed in recent hours."
He said the fact women and children were involved in the church bombings was particularly "egregious".
One million Australian holiday-makers travel to Indonesia every year.
Mr Dutton said Canberra would be doing whatever it could to support Jakarta.
Opposition Leader Bill Shorten and Labor's foreign affairs spokeswoman Penny Wong condemned the attacks.
"Such an attack has no basis in religion, and is an affront to peace-loving people of all faiths," they said in a joint statement.
"It is particularly concerning to hear reports of the attacks being carried out by a single family, which murdered its own children."
Former prime minister Kevin Rudd said the incidents were a "sobering reminder" of the new danger posed by Islamic State fighters returning from Syria and Iraq.
"Significant threat to Australians and westerners in SEA (South East Asian) region," he tweeted.
Last year, the Philippines scrambled to quash a five-month IS insurgency in Marawi.
Australia provided surveillance aircraft and has been training Filippino troops in urban combat.