Indonesian anti-terrorism authorities have arrested four more people suspected of having played a role in January's deadly bombings in Jakarta, claimed by Islamic State militants, officials said Wednesday.

National police spokesman Maj. Gen. Anton Charliyan was quoted by the Associated Press (AP) as saying that the suspects knew of the plot a month before the bombs ripped through downtown Jakarta on Jan. 14.

Six Indonesians, including four attackers, were killed in the explosions. Forty-three people have been arrested so far for the attacks, the AP reported.

Two of the suspects were nabbed in Central Java and two others in East Java, Charliyan said of the fresh arrests.

Authorities in the region have vowed to fight Muslim extremism in Southeast Asia, amid reports that some groups, including those in neighboring southern Philippines, had pledged allegiance to the Islamic State group, also known as ISIS.

Largely Muslim Indonesia has been combating extremism for years, and early in the past decade had struggled with the Jemaah Islamiyah, then known as al Qaeda's Asian tentacle. The Jemaah Islamiyah has been blamed for bombings in the resort island of Bali that left over 200 dead, many of them Western holidaymakers. 

Threats from that group have largely fizzled out, and authorities say it has been taken over by ISIS, which has been blamed for recent deadly attacks in the Middle East and in the West. The fear now is that Muslims from this region who fought alongside ISIS militants in the Middle East could return home to spread violence.

Malaysia is also predominantly Muslim and there have been cases of its citizens being involved in attacks, including in Mindanao island in southern Philippines, which has suffered under long years of Muslim insurgency. Malaysian Prime Minister Najib Razak, speaking in Saudi Arabia earlier this week, pledged to combat the terrorism menace in the region.