The U.N. envoy for Syria on Tuesday called the fight against jihadists in Syria a game changer, and said U.S. air strikes could even help ease humanitarian needs.

"In order to move at the moment there is obviously a game changer and the game changer is Daesh and the fight against Daesh," Staffan de Mistura told reporters at U.N. headquarters, using the Arabic acronym for the Islamic State group.

Police have shot dead a "known terror suspect" who stabbed two officers, a day after the Islamic State group called for Muslims to indiscriminately kill Australians, officials said Wednesday.

The 18-year-old, reportedly associated with the Islamic group Al-Furqan, was killed on Tuesday evening, having arrived at a police station on the outskirts of Melbourne to attend a "routine" interview.

When he finally managed to cross the Turkish border to find sanctuary from jihadists in Syria, Abdelaziz Temo looked for shade to find refuge from the sun and water to refresh himself.

He stopped in a small mosque in the Turkish border town of Suruc. But three days later, he has still not left the building as Turkey struggles to accommodate the influx of almost 140,000 Kurdish refugees.

Iran condemned the U.S.-led strikes on jihadist militants in Syria on Tuesday as a violation of the country's sovereignty.

"Any kind of military intervention in Syria without the demand of the government of this country and without abiding by international laws is not acceptable," Deputy Foreign Minister Hossein Amir-Abdollahian was quoted as saying by official news agency IRNA.

President Barack Obama will meet representatives of the five Middle Eastern nations that supported the first U.S. strikes in Syria later on Tuesday, his spokesman said.

Obama will see the officials from Saudi Arabia, Jordan, the UAE, Bahrain and Qatar after he arrives in New York for the United Nations General Assembly meetings, White House spokesman Josh Earnest told reporters on Air Force One.

It may be unable to prevent U.S.-led strikes on its territory, but Syria is hoping the military action against Islamic State jihadists will work to its advantage, analysts said.

On Tuesday, after the United States and its Arab allies bombarded numerous IS sites in Syria, the government in Damascus said it welcomed any international effort against "terrorism" and said it had been notified before the raids.

The brother-in-law of Mohamed Merah, the Al-Qaida-inspired gunman who went on a killing spree in 2012 that shocked France, was arrested at a Paris airport Tuesday on suspicion of having joined jihadists in Syria.

The man -- the husband of Merah's sister Souad, who herself is believed to be in Algeria -- was detained at Orly airport near Paris along with two other people, interior ministry sources said.

The jailed leader of Turkey's outlawed Kurdistan Workers Party (PKK) urged Kurds to join "all-out resistance" against Islamic State militants advancing on Kurdish areas in northern Syria, the pro-Kurdish Firat agency reported Tuesday.

IS extremists have closed in on the strategic Syrian town of Ain al-Arab near the Turkish border, called Kobane in Kurdish, and have seized dozens of villages in the past week, prompting an exodus of refugees into Turkey.

Syria's opposition National Coalition on Tuesday welcomed U.S.-led air strikes against the Islamic State (IS) group, but urged sustained pressure on President Bashar Assad's government.

Syria's Kurdish leadership also welcomed the strikes, as fighters on the ground tried to defend a key Kurdish town from a massive IS offensive.

British Prime Minister David Cameron is to hold talks with Iran's President Hassan Rouhani over unrest in Iraq and Syria, officials said Tuesday, the first meeting between the country's leaders since the 1979 Islamic Revolution.

The talks at the U.N. General Assembly in New York come as Western powers seek to build support for the fight against the Islamic State (IS) jihadist group, which holds swathes of territory in Iraq and Syria and has beheaded two U.S. journalists plus a British aid worker.