Australian authorities Tuesday dropped a terror charge against a teenager over an alleged Islamic State-inspired plot to attack Anzac Day commemorations honoring the war dead, citing insufficient evidence. 

Harun Causevic, 18, was arrested along with fellow teen Sevdet Ramden Besim in raids in Melbourne in April and both were charged with conspiring to commit a terrorist act.

Melbourne, Australia, is the world's most liveable city but conflict and terrorism have led to a fall in global urban living conditions more generally, according to a respected British study published Tuesday.

For the fifth year running, the Australian city came out on top of the annual Liveability Ranking study of 140 cities, conducted by the Economist Intelligence Unit, ahead of Austrian capital Vienna and Vancouver, Canada, which came out top in 2011.

A Melbourne man has been charged with attempting to leave for Iraq to fight with Kurdish forces against the Islamic State group, just weeks after another Australian was killed during a similar venture.

Jamie Williams, 28, is accused of preparing to enter a foreign country with the intention of engaging in hostile activities -- which carries a maximum penalty of life imprisonment.

Australia on Thursday announced a clearer terror alert system as the country faces what Prime Minister Tony Abbott called the worst extremist threat in its history, with the government outlining a long-term strategy to tackle the scourge.

The new system will be introduced later this year, subject to community consultation, with the new threat levels to be: certain, expected, probable, possible and not expected, which Abbott said would be much easier for the public to understand.

Australia's domestic spy agency Thursday played down concerns that maps shown in a media briefing revealing the source of homegrown fighters travelling to the Middle East were classified, after fears their publication was a security breach.

The maps, which revealed the Sydney and Melbourne suburbs where fighters heading to join jihadists came from, were photographed and filmed by journalists during a meeting Wednesday between Prime Minister Tony Abbott and spy chief Duncan Lewis.

Reports that a Lebanese-Australian terrorist, notorious for holding up the severed heads of Syrian victims, has been killed fighting in Iraq have raised the potential for his young family to be repatriated from the Middle East, Australia's foreign minister said on Tuesday.

Australian intelligence agencies were attempting to verify the recent deaths of Australians Khaled Sharrouf and Mohamed Elomar in the Islamic State-held city of Mosul in Iraq, Foreign Minister Julie Bishop said. Both men were seen in photographs posted on social media holding heads of Syrians.

Two Australian teenagers arrested last month on terror charges allegedly planned to run down  police officers with a car, behead them and then shoot other people, reports said Tuesday.

Two Melbourne men, Sevdet Besim and Harun Causevic, were charged with conspiring to commit a terrorist act, allegedly at an Anzac Day parade for Australia's soldiers on April 25.

A 39-year-old Lebanese national was killed at dawn in Melbourne, Australia after unknown assailants opened fire at him.

The state-run National News Agency reported on Sunday that Khaled Yehya Abou Hasna was the victim.

Two men were arrested in Melbourne on Saturday for allegedly planning an Islamic State-inspired attack at Anzac Day commemorations honoring soldiers who fought and died for Australia -- the country's most important national event.

Seven search warrants were executed in the country's second largest city by a joint counter-terrorism team of 200 officers, two months after Prime Minister Tony Abbott warned the threat from home-grown extremists was worsening.

A nightclub bouncer who reportedly became a terror group leader. A man who tweeted a photo of his young son clutching a severed head. A teenager who is believed to have turned suicide bomber, and others suspected of attempting to travel to Syria to join the Islamic State movement. All of them, Australian.

The London-based International Center for the Study of Radicalization and Political Violence reports that between 100 and 250 Australians have joined Sunni militants in Iraq and Syria. Given Australia's vast distance from the region and its population of just 24 million, it is a remarkable number. The center estimates that about 100 fighters came from the United States, which has more than 13 times as many people as Australia.