Malaysian police have arrested four men who they said were planning to attack temples and churches, and kill high-profile individuals, to avenge the death of a Malay-Muslim fireman who died from injuries sustained at the carpark of a Hindu temple last November.

Malaysia's national police chief Abdul Hamid Bador said the men - two ethnic Rohingya, an Indonesian and a Malaysian - were arrested in a series of operations between May 5 and May 7 in three different places.

"One of the group's main objectives was to avenge the death of fireman Adib... (and) they were planning to kill high-profile individuals," the new Inspector-General of Police told reporters at a news conference yesterday.

Datuk Seri Abdul Hamid declined to reveal the identities of the VIPs, citing it as "very sensitive".

The death of fireman Muhammad Adib Mohd Kassim, 24, has become a rallying call for some Malaysian Muslims, including those in the Malay-Muslim opposition parties, who feel his death at the Seafield Sri Maha Mariamman Temple in Subang Jaya has not been addressed by the government.

Mr Adib was critically injured in the early morning of Nov 27 last year after he and his team members responded to an emergency call at the temple, where a riot had taken place earlier.

He was taken to hospital and later transferred to the National Heart Institute for further treatment, but died on Dec 17.

No one has been charged over the death, and there is an ongoing inquest into the incident.

The police's counter-terrorism division seized six improvised explosive devices (IEDs) in one of the swoops which they believe the men were planning to use in attacks on entertainment outlets and houses of worship in the Klang Valley during the Muslim holy month of Ramadan.

In the first arrest, the police detained a 34-year-old Malaysian labourer in Kuala Berang, Terengganu, on May 5.

"He is suspected to be the mastermind of the cell. He planned to bomb temples and churches, as well as entertainment outlets," said Mr Abdul Hamid.

Police seized a 9mm CZ pistol with 15 bullets from the suspect and six IEDs measuring 18cm long. "The bombs were smuggled from a neighbouring country," said the police chief.

On May 7, two Rohingya men, aged 20 and 25, were arrested in Kuala Lumpur, and a 49-year-old Indonesian man was later detained in Subang Jaya, Selangor.

Police said one of the Rohingya men admitted to supporting the Arakan Rohingya Salvation Army, an armed group that claims to be fighting on behalf of Myanmar's beleaguered Rohingya minority. The man was also planning to attack the Myanmar Embassy in Kuala Lumpur, Mr Abdul Hamid said.

The Indonesian was planning to fight in Syria.

"All four suspects communicated via WhatsApp, and they received instruction from a Malaysian national who is still in Syria. They are being detained under the Security Offences (Special Measures) Act," the police chief said.

Mr Abdul Hamid said the militant group was established in January. The Malaysian police are also seeking three more members of the group.

Since 2013, Malaysia has arrested nearly 400 people for suspected links to terrorism.