President Barack Obama vowed Wednesday that the United States would not be intimidated by the beheading of a second American reporter but acknowledged the fight against the jihadists would take time.

Obama pledged that justice would be done to the Islamic State (IS) killers of 31-year-old reporter Steven Sotloff, wherever they hid and however long it took.

President Barack Obama on Tuesday ordered about 350 more US troops to Baghdad to safeguard American diplomats in the Iraqi capital, increasing the U.S. military presence to more than 1,000 forces.

The move comes after a request last month from the State Department for additional U.S. troops to bolster security for the US embassy and other facilities in Iraq, where Islamic State (IS) extremists have seized territory in the north and west of the country.

From Tallinn to Warsaw, Russian moves in Ukraine are sparking grave concern across a region deeply scarred by war and decades of Soviet occupation on the eve of a landmark visit by U.S. President Barack Obama.

"I'm very worried mainly because every time it seems like it can't get any worse, it does," says Helen Sildna, 35, a music festival impresario in Estonia's capital Tallinn where Obama will touch down Wednesday en route to a NATO summit in Wales.

He doesn't bluster and he doesn't strut and President Barack Obama certainly isn't panicking, though he admits it feels like the world is falling apart.

But Obama's cool-in-a-crisis style and disdain for the impulsive use of military force is fueling criticism of his leadership, as crises stagger the Middle East and Ukraine.

King Abdullah of Saudi Arabia has warned that the West will be the next target of the jihadists sweeping through Syria and Iraq, unless there is "rapid" action.

Barack Obama's Democrats are walking a tightrope 10 weeks before U.S. congressional elections: do they solicit the unpopular president's support or shun him as they try to maintain their Senate majority?

U.S. Secretary of State John Kerry called Friday for a global coalition of nations to combat Islamic State jihadists' "genocidal agenda" in Syria and Northern Iraq.

U.S. President Barack Obama admitted Thursday that he still does not have a strategy to fight Islamic State jihadists in Syria, as the militants boasted they had executed scores of Syrian troops -- the latest in a string of atrocities that have shocked the world.

Dampening hopes of imminent air strikes in Syria, Obama said he was still developing a comprehensive plan to defeat IS, which has also overrun large swathes of Iraq.

U.S. President Barack Obama will meet top national security aides on Thursday, amid accusations Russia has sent troops into Ukraine and as he deliberates possible strikes in Syria against Islamic State militants.

Obama will gather members of his National Security Council, which includes the secretaries of state and defense, intelligence chiefs and top military brass, in the secure Situation Room of the White House at 2000 GMT, officials said.

U.S. spy agencies face a difficult task in tracking Islamic jihadists in Syria, as Washington lacks a robust network of informants and faces threats to its drone fleet, experts and former officials say.