Sydney (AFP) - The leader of the Sydney mosque attended by a 15-year-old who killed a police worker has called for an end to violent extremism, saying Friday that Muslims who reject Australian values should leave the country.

Radicalised Farhad Jabar, who shot dead the 58-year-old last week while reportedly shouting religious slogans before dying in a gunbattle with police, was a regular at the mosque in the western multi-cultural Parramatta district.

Mosque chairman Neil El-Kadomi explained to reporters what he had told the faithful at morning prayers and ahead of a planned evening protest by right-wingers to close the building down.

"I said you waited long time to come to this country. You should not abuse the privilege you are Australian, which is very important.

"Get out. We do not need scumbags in the community.

"We reject terrorism."

Kadomi said Muslim youth needed education, adding that Jabar was too young "to know what he was doing".

CCTV footage from Parramatta mosque reportedly shows Jabar meeting several men there on the day of the killing, although police have not confirmed this.

Prime Minister Malcolm Turnbull also advised people to leave if Australian values were "unpalatable".

"It is not compulsory to live in Australia," he told a press conference urging Australians not to go down the path of violent extremism.

"If you find Australian values, you know, unpalatable, then there's a big wide world out there and people have got freedom of movement."

Turnbull, who met earlier in the day with figures from the Muslim community, asked his countrymen to "call out hatred" saying "violent extremism is a challenge to the most fundamental Australian values".

"The success of our society is founded on mutual respect and we have to recognise that people who preach hatred, preach extremism, are undermining the success of this extraordinary country," he said.

Friday also saw the Grand Mufti of Australia, Ibrahim Abu Mohamed, and other community and religious leaders address the media amid rising community tensions.

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Mohamed said violent religious extremism was a rare but serious issue threatening the whole community.

"Sadly, a very, very small number of Australians of Muslim faith have chosen this path," he said.

Police issued a warning ahead of the planned Parramatta protest called by a far-right group.

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

Canberra is concerned at the prospect of lone-wolf attacks by individuals inspired by groups such as Islamic State, and has cracked down on Australians attempting to travel to conflict zones including Syria and Iraq.

The authorities lifted their terror threat alert to high a year ago, introduced new national security laws and have conducted several counter-terrorism raids.

In September 2014, Melbourne police shot dead a "known terror suspect" who stabbed two officers and in December, Iranian-born self-styled cleric Man Haron Monis and two hostages were killed following a 17-hour siege at a Sydney cafe.