U.S. Republicans offered strident reaction Thursday to President Barack Obama's unilateral plan to bring millions of undocumented non-citizens out of the shadows and make them eligible for work permits.

"That's just not how our democracy works," House Speaker John Boehner said in a statement after the White House unveiled details of Obama's plan, which lifts the threat of deportation for up to five million undocumented migrants.

Syrian President Bashar Assad said on Thursday that "international cooperation" was necessary to crush the Islamic State group, which is the target of a U.S.-led campaign.

"The region is going through decisive times" and the most important factor in determining the outcome is whether there is "real and sincere international cooperation" against the jihadists, Assad said.

U.S. President Barack Obama has ordered a comprehensive review of U.S. policy on "overseas terrorist-related" hostage cases, a letter from the Pentagon has revealed.

The missive surfaced just one day after the Islamic State group posted the beheading of yet another Western hostage, U.S. aid worker Peter Kassig, in a grisly online video.

Scores of Myanmar students rallied illegally in Yangon Monday against a new education bill they describe as undemocratic, the latest in a series of protests that began during a visit by U.S. President Barack Obama.

Young activists, some holding banners reading "We need Academic Freedom" and "Fight for Democratic Education", staged a peaceful march across the city center to call for the education system to be reformed.

A top Saudi Arabian official who begins a visit to the United States on Tuesday will seek to strengthen support for the kingdom's powerful National Guard forces, official media said.

The Guard is a parallel army of around 200,000 men whose duties include combating "terrorism".

Australia arranged a warm and fuzzy welcome for the world's most powerful leaders at this weekend's G20 summit with a campaign dubbed "koala diplomacy", in which top politicians cuddled the shy native marsupials.

There may have been sharp differences during policy discussions but G20 leaders were unanimous in their desire to be photographed with the furry grey animals, which were brought in from a local wildlife park for the summit.

Israel's Prime Minister Benjamin Netanyahu expressed support Sunday for the U.S. fight against Islamic State militants, but cautioned against any softening toward Iran.

"We want them both to lose. The last thing we want is to have any one of them get weapons of mass destruction," Netanyahu said in an interview with CBS Face the Nation.

Sanctions-hit Russia risks deeper isolation from the global community unless it takes a different path on Ukraine, U.S. President Barack Obama said Sunday at the end of a stormy G20 summit.

Obama said if President Vladimir Putin "continues down the path that he is on, violating international law, providing heavy arms to the separatists in Ukraine.... then the isolation that Russia is currently experiencing will continue".

U.S. President Barack Obama on Sunday rejected any alliance with Bashar Assad against the Islamic State group, arguing that the Syrian ruler was illegitimate and that any such pact would backfire.

"Assad has ruthlessly murdered hundreds of thousands of his citizens. As a consequence, he has completely lost legitimacy with the majority of the country," Obama told reporters after a G20 summit in Brisbane. 

Iran and six world powers begin a final round of talks in Vienna on Tuesday aiming to overcome significant remaining differences and agree a historic nuclear deal by a November 24 deadline.

"There's still a big gap. We may not be able to get there," U.S. President Barack Obama warned last Sunday.