A Sydney man accused of travelling to Syria to fight alongside Al-Qaeda affiliate Jabhat al-Nusra has alleged links to two other men who are also under the watch of counter terrorism police.

State and federal police from the Joint Counter Terrorism Team have arrested Mehmet Biber, 24, and a 17-year old boy on suspicion of breaching foreign fighter laws.

Biber was arrested at Birrong this morning over allegations he travelled to Syria to fight alongside Jabhat al-Nusra in July 2013.

Counter terrorism police will allege he travelled to the conflict zone with the help of Islamic State supporter Hamdi Al Qudsi.

Al Qudsi was sentenced to a minimum of six years in prison for his role helping seven young Australian men travel to fight with extremist jihadi groups in Syria, including the forerunners of Islamic State.

The national manager of counter-terrorism for the Australian Federal Police, Neil Gaughan, said the 17-year old boy arrested this morning attempted to travel to the region to fight for IS in January 2015.

"Obviously we've moved as quickly as we can in relation to this matter due to the risk that these people pose, but also in relation to the ideology that they possess, and that will be something we will be alleging in court later today," Mr Gaughan said.

"This has been a protracted investigation and a very difficult one.

"Evidence collection from Syria is extremely difficult."

Police from the Joint Counter Terrorism Team confirmed they executed a number of raids this morning as part of an ongoing investigation into alleged foreign incursion offences.

Mehmet Biber, pictured with three friends in an image from Facebook, will reappear in court next month. ( Facebook: Fairfax Media )

Suspects face court

Biber appeared briefly in Parramatta Local Court today and was refused bail.

He is due to appear again, via video link, on December 15.

The 17-year old faced foreign incursion charges at the Parramatta Children's Court today where bail was also refused.

His lawyers chose not to apply for bail on this occasion but told the court they may apply for it at a later date.

The matter was adjourned until a date in December, when the boy is due to appear via video link.

Police can't do it alone: Deputy Commissioner

Deputy Commissioner Catherine Burn said police were searching for prohibited weapons and firearms when they searched the homes at Merrylands, Horningsea Park, Bass Hill and Miller.

"Community safety is our priority, so even if this might have taken two or three years to put somebody before a court, the safety of the community has been our number one priority at all times in regards to this investigation," Deputy Commissioner Burn said.

"We have a juvenile who appears to be involved, and we will allege is involved potentially in wanting to engage in hostile activities, and this is a continuing concern for us.

"This is not a law enforcement issue alone. We can't do this alone.

"We have to work with everybody so we can eliminate what we are seeing with some of our young people."

The ABC has been told a property raided at Merrylands is the home of fundamentalist Islamic preacher Junaid Thorne, who is understood to be an associate of Biber and the 17-year-old.

Thorne spent four months in Supermax in 2014 after he was convicted of using a false name to book a domestic flight.

A house in Merrylands in Sydney's west was raided by counter-terrorism police today. ( ABC News: Jackson Vernon )

Government making changes to terror laws

Prime Minister Malcolm Turnbull said the arrests showed the threat Australia was facing.

Addressing media in Sydney, Mr Turnbull highlighted the need to update counter-terror legislation.

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"We have to keep on adapting and modernising our tactics, our legislation to deal with these evolving threats," he said.

"We must not underestimate our enemies: they are agile, they are tech savvy, and we have to move as quickly as them."

Mr Turnbull said the Government was reforming the control order regime and laws relating to post-sentence detention of terrorists.

"We have vital legislation that we need to be passed by the Parliament this year," he said.

He said radicalisation would also remain a priority.

"The disturbing feature that we are seeing increasingly is very young people who have not been on the radar screen of any of our current terrorist agencies, state or federal, are becoming very quickly radicalised and either attempting or undertaking terrorist acts," he said.

"This is a key priority of the Government, we are keenly focused on it."