U.S. President Barack Obama said Washington was not ready to open an embassy in Iran due to differences over nuclear policy, a position that contrasts with his new approach to Cuba.

"I never say never, but I think these things have to go in steps," Obama said in an interview with National Public Radio that aired Monday, regarding re-opening the long-shuttered U.S. mission in Tehran.

NATO formally ended its war in Afghanistan on Sunday, holding a low-key ceremony in Kabul after 13 years of conflict that have left the country in the grip of worsening insurgent violence.

The event was arranged in secret due to the threat of Taliban strikes in the Afghan capital, which has been hit by repeated suicide bombings and gun attacks over recent years.

Tens of thousands of officers paid tribute to one of their own at a New York funeral Saturday, as emotions ran high over recent protests against police violence.

But in a sign of the strain between New York's police force and its mayor, thrown into sharp relief since the officers were shot last week, numerous officers turned their backs outside as Bill de Blasio began to speak.

Former U.S. president George H.W. Bush will stay at a Texas hospital through the weekend after experiencing breathing problems, but his spokesman said Saturday he could be discharged soon.

Bush, 90, was admitted late Tuesday to Houston Methodist Hospital. He received family visits on Christmas Day, and his spokesman Jim McGrath said he was making progress.

President Barack Obama in a Christmas Day speech to U.S. troops stationed in Hawaii hailed their "extraordinary dedication and sacrifices," as NATO prepares to wrap up its combat mission in Afghanistan.

After a morning of exchanging gifts with family members during their annual year-end vacation in his birth state, the president and First Lady Michelle Obama paid a visit late Thursday to a Marine Corps base in Hawaii.

The United States, Japan and South Korea have agreed a rare trilateral military arrangement on intelligence sharing about North Korea's nuclear and missile programs, officials said Friday.

The deal, which is to be signed on Monday according to South Korea's defense ministry, comes at a time of heightened concern about North Korea's nuclear and missile programs, which are seen as a major security concern in the Pacific region and beyond.

Jordan vowed Thursday to make every effort to save a pilot captured by the Islamic State group in Syria as Washington denied claims the jihadists had shot down his warplane.

Maaz al-Kassasbeh, a 26-year-old first lieutenant in the Jordanian air force, was captured by IS on Wednesday after his F-16 jet crashed while on a mission against the jihadists over northern Syria.

A U.S. federal judge handed a victory to President Barack Obama late Tuesday, throwing out a lawsuit over controversial actions he took last month shielding millions of undocumented migrants from deportation.

The suit brought by Joseph Arpaio, the conservative sheriff of Maricopa County, Arizona, challenging the constitutionality of the president's actions, was dismissed by Judge Beryl Howell.

Five Americans have been charged in connection with a plot to sell 153 guns and smuggle them into New York in carry-on bags on 17 commercial flights, prosecutors said Tuesday.

The airline security breach put hundreds of travelers at risk and was allegedly aided by a Delta Airlines agent in Atlanta, who carried the weapons past security checks, officials said.

Former President George H.W. Bush has been taken to a Houston hospital after experiencing a shortness of breath.

Spokesman Jim McGrath said in a statement that Bush was taken by ambulance to Houston Methodist Hospital on Tuesday evening as a precaution.