Barack Obama delivered a forceful plea Tuesday for Hillary Clinton to succeed him as president, praising the character of his former secretary of state whose horizon brightened after the FBI recommended no charges be filed over her email scandal.

Obama, returning to a swing state that helped elect him in 2008, laid out a passionate, compelling case declaring he is "ready to pass the baton" to Clinton and urging voters to make her the nation's first female commander in chief.

President Barack Obama on Wednesday offered US security assistance to Turkey after 41 people were killed in a suicide assault on Istanbul airport, the latest in a string of attacks to rock the US ally.

Obama telephoned President Recep Tayyip Erdogan "to express his deep condolences on behalf of the American people," White House spokesman Josh Earnest told reporters traveling with the US leader to a summit in Ottawa.

The death toll from flooding in the U.S. state of West Virginia rose to 24, as President Barack Obama declared a major disaster, releasing federal aid for the hardest-hit areas.

Days of heavy rain, especially on Thursday and Friday, caused massive flooding in the state, where high waters have washed away cars, trapped hundreds and cut power to large areas.

U.S. President Barack Obama landed in Vietnam late Sunday for a landmark visit capping two decades of rapprochement between the former wartime foes, as both countries look to push trade and check Beijing's growing assertiveness in the South China Sea.

President Barack Obama on Friday warned the White House race is not a "reality show" and called for Donald Trump's record to be held to close scrutiny as the billionaire seeks to rally divided Republicans behind him.

With Trump seizing the mantle of presumptive Republican nominee this week after his rivals exited the race, debate has turned to whether he will be able to rally the party faithful behind him between now and November.

U.S. President Barack Obama has hailed German Chancellor Angela Merkel's "courageous" leadership in opening doors to migrants fleeing the Syrian conflict.

"I believe that Chancellor Merkel's approach to the refugee crisis -- and that of many Germans -- has been courageous. She's demonstrated real political and moral leadership," Obama said in an interview published Saturday with German daily Bild.

U.S. President Barack Obama said Thursday that Washington and Gulf Arab states were united against the Islamic State group as he sought to overcome strains on Iran to boost efforts against the jihadists.

In Riyadh for talks hosted by Tehran's arch-rival Saudi Arabia, Obama said the United States still has "serious concerns" about Iran, but insisted no country has an interest in conflict with the Shiite power.

Eleven non-governmental organizations have called on U.S. President Barack Obama to help free human rights defenders in Gulf monarchies, ahead of a summit with their leaders later this month.

In an open letter published Saturday by the Gulf Center for Human Rights (GCHR), signatories urged Obama "to press for the release of all detained human rights defenders across the Gulf region who are imprisoned solely due to their peaceful and legitimate human rights work".

U.S. President Barack Obama said on Friday it will take time for Iran to rejoin the global economy, as the country's leadership and citizens express unease that a sanctions windfall has been slow to materialize.

"It will take time for Iran to reintegrate into the global economy, but Iran is already beginning to see the benefit of this deal," Obama said at a meeting of world powers in Washington.

President Barack Obama on Saturday urged Americans not to stigmatize Muslims following this week's deadly attacks in Brussels, saying that doing so is "counterproductive" in the fight against radical Islam.

In his weekly media address, Obama said Muslim-Americans are "our most important partners in the nation's fight against those who would wage violent jihad.