The tensions follow last Friday's shooting of NSW Police employee Curtis Cheng and raids at premises around Sydney during the week. 

Marsden Street, between George and Macquarie streets, may be closed between 4pm and 7pm as a result of a police operation relating to the planned protest activity, police said. 

Superintendent Wayne Cox, Commander of Parramatta Local Area Command, says that police have not authorised any formal applications for public assemblies in Parramatta on Friday. 

Parramatta Mosque chairman Neil el-Kadomi said he would use the prayers to ask the community to "look after the youth" as Muslims began arriving for Friday prayers.

The mosque was the last place 15-year-old Farhad Jabar visited before gunning down Mr Cheng 500 metres away last week.

"Listen to them, talk to them, advise them," Mr Kadomi said as he arrived at the mosque.

"We need to educate the youth, do courses in the mosque and in schools," he said.

He said Farhad Jabar had been so young that "he didn't know what he was doing".

The fact that he just stood there after the shooting showed "he was in a dilemma", Mr Kadomi said.

He denied that his mosque was involved with extremist teachings and said that if members of his congregation were engaging in such teachings he would refer them immediately to police.

"We live in Australia. Lots of people are dying on boats trying to get here - you are here. Australia gives us lots of benefits, there's opportunity and you are allowed to practise your religion freely," he said.

He was joined by Jeremy Jones, director of community relations for the Australia Israel Jewish Affairs Council, who had been in Parramatta to lay flowers outside NSW Police headquarters as part of an inter-faith group.

"I am here to express solidarity with Neil and to strengthen multiculturalism against extremism," he said. 

"When you are involved with others and having a dialogue about what it means to be a good Christian, Jew or Muslim, you don't give extremism a chance," he said.

But the mood remained tense outside the mosque. At least two media outlets had received threats warning that their reporters would be attacked with knives outside the mosque and police were patrolling the block around the building.

Mr Kadomi said he was expecting about 1000 worshippers and had received many phone calls after Fairfax Media reported he would tell those who did not respect Australian values to leave.

Right-wing threats

There are also fears of clashes with right-wing groups later in the day.

The leader of the anti-Islamic Party for Freedom, Nick Folkes, has invited people to protest against the mosque's existence while Mr Kadomi worships in the prayer hall, although their rally is planned for later in the day at 5pm.

"The high-maintenance Islamic community needs constant monitoring to prevent further terrorist attacks," Mr Folkes said.

A police spokesman said they had rejected Mr Folkes' application for the protest.

"NSW Police want to remind any member of the public against engaging in reprisal actions or inciting violence against any community group or individuals," Superintendent Cox said.

"Anyone engaging in this type of unlawful behaviour can be charged and prosecuted.

"As police, our message is that any act of violence, regardless of the motivation will not be tolerated, and will be treated as the serious offence that it is."

"Equally the rights of citizen's to hold peaceful assemblies are balanced with other rights including the undertaking of lawful business activities and the safety and security of the broader community," Superintendent Cox said. 

CCTV footage from the mosque showed Jabar at prayers and in the company of four other people.

Three were known to police and, in raids this week, they were taken into custody and interviewed. Three were released, but the Australian Federal Police have successfully applied to hold the 18-year-old for another 100 hours without charge.

Mr Kadomi told Fairfax Media before his sermon that those who did not respect the law and Australian values would be expelled from the Islamic community in Parramatta.

"We live in this country, you must respect it," he said. "If you don't like it, leave."

"Farhad was a real wake-up call," he said. "To anyone who has crime in mind, if you come to this mosque we will tell the police."

NOTE: An earlier version of this story was changed for legal reasons.