Police have arrested a slew of suspected terrorists in a nationwide crackdown against members and supporters of the Islamic State terror group.

According to highly placed sources, Bukit Aman counter-terrorism operatives picked up the men and women in a series of special operations, which have been ongoing since mid-last month.

It was learnt the operation was intensified after the May 17 deadly terror attack on Ulu Tiram police station in Johor, which saw two police officers killed while another seriously injured.

The sources were reluctant to reveal the exact number of arrests but hinted that more than 20 men and women have been rounded up to date.

They include several individuals suspected to be members of a terror cell and connected to an alleged bomb maker in Bagan Serai, Perak, who was charged in court earlier this month.

"Counter-terrorism police officers arrested more than six suspects yesterday.

"They were picked up in a simultaneous operation at several locations across the country, over suspicion of being involved with IS and posing possible threat to the public.

"Initial investigation revealed that these individuals were connected to the Bagan Serai suspect," claimed a source, who spoke on condition of anonymity.

Malaysiakini has contacted Deputy Inspector-General of Police Ayob Khan Mydin Pitchay for comments as Inspector-General of Police Razarudin Husain is on leave to perform haj.

On June 11, a factory operator was reportedly charged at the Sessions Court in Taiping, Perak with three counts of criminal offences related to terrorism.

The alleged offences include aiding IS by keeping explosive materials for the terror group's activities, according to Free Malaysia Today.

Two days later, authorities charged another man with an alleged link to IS. The gardener, who was accused in Muar of being in possession of IS-related items and supporting the group, has previously been jailed twice over terrorism-related offences, according to the New Straits Times.

More to be charged

Sources claimed that the factory operator and the gardener knew each other, and police have since picked up six others, including a woman, several weeks ago, whom they believe to be connected to the two.

The suspects were allegedly influenced by IS ideology and were planning attacks on several locations in the country, said a source.

Authorities planned to charge the six suspects in court tomorrow, the security agency source added.

"They are expected to be charged separately in courts across several states.

"Three of them including the woman will be taken to the Johor Bharu Sessions Court, while the rest are to be charged in Kuala Lumpur, Kuala Kubu Baharu (Selangor), and Segamat (Johor)."

Malaysiakini learnt that the charges being prepared against the suspects ranged from soliciting and giving support to IS, to being in possession of terrorism-related items and supporting the commission of a terrorist act.

On May 17, two police officers were killed when a lone attacker set upon them at the Ulu Tiram police station.

The youth used a machete to attack and kill one of the officers. He then stole his firearms before getting into a shootout with other police officers. It ended with the attacker shot dead, while a third police officer was seriously injured.

Police had initially suspected the attacker was influenced by Jemaah Islamiyah, of which his father is a former member, but later established that he was allegedly indoctrinated by IS ideology.

READ MORE: KINIGUIDE | Ulu Tiram terror attack - Jemaah Islamiyah in Malaysia

The last time IS had successfully carried out an attack in Malaysia was in 2016 when suspected members of the group set off a hand grenade at Movida Bar in Puchong.

Following the Ulu Tiram incident, Bukit Aman raided the attacker's house and arrested five of his family members.

The family members, including the attacker's father, had since been charged in court with allegedly spreading the IS ideology.

Last week, Malaysiakini reported that security experts expressed concerns over lingering threats posed by sympathisers of the terror organisation, despite it no longer having a significant territorial grip.

COMMENT | Playing down terror attacks does no one any favours

COMMENT | Playing down terror attacks does no one any favours

IS still a lurking danger, security experts warn

IS still a lurking danger, security experts warn

After Ulu Tiram attack, groups in solidarity with police against 'terrorism'

After Ulu Tiram attack, groups in solidarity with police against 'terrorism'

S'pore PM: Attack on Johor police station shows terrorism threat still high

S'pore PM: Attack on Johor police station shows terrorism threat still high