Republican frontrunner Donald Trump called Sunday for the return of waterboarding, a near-drowning interrogation technique widely denounced as torture, saying it was "peanuts" compared to what Islamic State is doing.

It was the latest in a series of inflammatory Trump responses to the threat of terrorism in the wake of the Paris attacks that appear to have bolstered his poll numbers.

Officials in a Pakistani city hit by sectarian riots called a meeting of religious clerics Sunday to defuse tensions as scores of Ahmadi Muslims reportedly fled after a weekend of violence.

The unrest began Friday when an angry mob in the eastern city of Jhelum torched a factory after one of its employees, a member of the persecuted Ahmadi sect, was accused of committing blasphemy by burning pages of the Koran. 

At least four people were killed and others wounded, including police, in the latest clashes in months of unrest in Burundi's troubled capital, police said Sunday.

Heavy gunfire and grenade explosions were heard overnight Saturday, with the bodies of four people found on the streets on Sunday morning. Residents said gun battles raged for around two hours.

Some two million Sudanese children under five suffer from malnutrition every year, UNICEF's representative said on Sunday, urging the international community to boost funding to tackle the problem.

Of those two million, nearly 550,000 children have life-threatening severe acute malnutrition, with many of those affected living in the underdeveloped east and conflict-hit Darfur region.

A Singapore Airlines (SIA) flight from San Francisco via Hong Kong received a bomb threat but arrived without incident in Singapore on Sunday, police said.

Police said in a statement they conducted checks but nothing suspicious was found on the plane or its passengers.

Iran on Sunday confirmed that it had sentenced Iranian-American Washington Post reporter Jason Rezaian to an unspecified prison term following his conviction last month on charges including espionage.

"The verdict includes a prison term," judiciary spokesman Gholamhossein Mohseni Ejeie was quoted as saying by the official IRNA news agency. 

Crimea declared a state of emergency on Sunday after its main electricity lines from Ukraine were blown up, leaving the Russian-annexed peninsula in darkness after the second such attack in as many days.

More than 1.6 million people are without power, water supplies to high-rise buildings have stopped and cable and mobile Internet is down.

The brother of wanted Paris terror suspect Salah Abdeslam said Sunday he believed he decided at the very last moment not to go through with an attack.

Belgium has launched a huge manhunt for the 26-year-old who is believed to be the only surviving member of the gang of jihadists behind the massacre in the French capital.

Afghan Taliban militants on Saturday kidnapped at least seven members of the minority Shiite Hazara community after a dispute over sheep, local authorities said.

Gunmen stopped three buses at dawn between Shah Joy and Qalat in the volatile Zabul province, first taking 17 hostages before releasing nine, local leader Wazir Mohammed Jawadi said.

U.S. President Barack Obama called Sunday for resolve in the face of heightened jihadist threats, insisting panicked citizens must not succumb to fear and urging world leaders not to abandon a climate summit in Paris.

With Brussels in lockdown, cities from Beirut to Bamako reeling from attacks, and Americans jittery that they too may come under assault, Obama said the world must show steel.