Indonesia is set to approve a law allowing authorities to jail for up to 15 years citizens coming home after joining militant groups abroad, lawmakers said on Wednesday.

The tightening of anti-terrorism laws in the world's largest Muslim-majority country comes as concern grows about the spread of influence of Islamic State, and fears it wants a foothold in Southeast Asia as it loses territory in the Middle East.

"The new criminal code adopts the principle of universality, which means that wherever an Indonesian citizen commits a crime, they can be legally processed in Indonesia," said lawmaker Arsul Sani, referring to terrorism.

"They can face up to 15 years in prison," he said.

The legislation was likely to be approved in September, legislators said.

Law enforcement agencies have long complained of their inability to deal with people who have travelled abroad to join Islamic State and then returned home.

Authorities believe Islamic State has thousands of sympathizers in Indonesia.

Hundreds of Indonesian men, women, and children are thought to have travelled to Syria in recent years, and authorities believe about 400 Indonesians have joined Islamic State.

Dozens are believed to have returned to Southeast Asia.

The region, with a population of about 600 million, has suffered occasional militant attacks over the years since the Sept. 11, 2001, attacks on the United States.

In particular, the Philippines and Indonesia have seen attacks by militants claiming allegiance to al Qaeda, and more recently to Islamic State.

Government forces in the predominantly Christian Philippines have been battling militants linked to Islamic State in a town in its Muslim-majority south for the past month.

In Indonesia, a suicide bomb attack by Islamic State-inspired militants at a bus station last month killed three police officers.

Indonesia's tightening of its security laws is part of a revision that President Joko Widodo has urged to meet the new danger.

Changes will broaden the definition of terrorism and give police powers to detain suspects without trial for longer.

Police will also be empowered to arrest people for hate speech or for spreading radical content, as well as those taking part in paramilitary training or joining proscribed groups.

National police chief Tito Karnavian said on Wednesday security has been tightened ahead of this weekend's Eid al-Fitr festival that marks the end of the Muslim fasting month of Ramadan. He said 38 suspected militants had been detained in recent weeks.

Neighbouring Malaysia and Singapore already have tough internal security laws that allow for lengthy detention without trial.

Alarmed by the surge of violence in the southern Philippines, Indonesia, Malaysia, and the Philippines this week launched joint air and sea patrols to prevent militants from crossing their common borders.