Timeline: Australia's terror threat

Legislation and security have been tightened in recent months, amid growing concerns over foreign fighters

Concern has been growing in Australia in recent months over the effect on domestic security of Australian nationals fighting with or sympathising with Islamist militant groups in Iraq and Syria. The BBC looks at how events - and related legislation - have developed.

20 April 2015: British police say a 14-year-old boy from northern England was arrested on 2 April in connection with an alleged plot to target an Anzac memorial event in Australia. The same alleged plot had seen five teenagers arrested in Melbourne on 18 April, including Sevdet Besim, 18, who was charged with conspiring to commit a terrorist act.

2 March: Australia makes it illegal for its citizens to travel to IS-held Mosul in Iraq without "legitimate" reason.

23 Feb: PM Tony Abbott announces plans to toughen citizenship laws and clamp down on those inciting hatred.

11 Feb: Police arrest and charge two men with planning to carry out an imminent attack, saying they seized a hunting knife, an IS flag and a video describing an attack.

24 Dec 2014: Counter-terrorism police in Sydney arrest two men, charging one with possession of documents designed to facilitate a terrorist attack.

15-16 Dec: Gunman Man Haron Monis, a self-styled cleric originally from Iran, takes 17 people hostage in a cafe in the centre of Sydney. Monis and two hostages are killed after a 16-hour siege. His former lawyer describes him as "unhinged" but not a jihadist.

The siege at the Lindt Cafe in Sydney lasted 16 hours

4 Dec: Australia bans its citizens from travelling to the Syrian province of Raqqa, stronghold of IS.

30 Oct: Parliament completes approval of a security law that creates a new offence of "advocating terrorism" and seeks to ban Australians from travelling to certain conflict areas.

29 Oct: The government says it is trying to confirm reports that the most senior Australian member of IS, Mohammad Ali Baryalei, has been killed in Syria.

8 Oct: Mr Abbott proposes ban on foreign "hate preachers".

3 Oct: Australia approves air strikes against IS.

23 Sep: A teenager described as a "known terror suspect" is shot dead after he stabs two police officers at a Melbourne police station.

Two police officers were stabbed by a Muslim teenager at Endeavour Hills police station

18 Sep: Australia carries out what it calls its biggest counter-terrorism raid; Mr Abbott later confirms this was linked to an alleged plot by Australia-based individuals to kill a randomly selected member of the public. The intelligence is reported to have come from an intercepted telephone call involving an Australian fighter with Islamic State (IS) in Syria.

14 Sep: Prime Minister Tony Abbott commits 600 troops to fight against Islamic State, as part of a multilateral effort.

12 Sep: Australia raises terror threat level from medium to high, for the first time since the system was introduced in 2003.

10 Sep: Brisbane Islamic centre raided; two charged with terrorism offences.

27 Aug: New counter-terrorism units set up in airports to stop departing fighters. Separately, director general of Australia's spy agency, David Irvine, says 15 Australian militants have died fighting in Iraq and Syria. One hundred or more people in Australia are "actively supporting" militant groups by recruiting new fighters and providing funds, he says.

11 Aug: Image emerges of young son of Australian militant fighter holding severed head of Syrian soldier.

5 Aug: New legislation aimed at preventing people going to fight with Islamist groups announced.

21 July 2014: Officials say Australian suicide bomber behind an attack in Iraq; concern grows over the number of Australians fighting for Islamist militant groups in the Middle East and the effect of them and their supporters and sympathisers on domestic security.