The White House leads tributes to former New York City Mayor Ed Koch, who has died at the age of 88.

Harvard University imposes academic sanctions on dozens of students for cheating in a final exam, a dean says in an email to students.

Rescue work after a deadly blast at the headquarters of Mexico's Pemex oil company enters its most dangerous phase, says the attorney general.

The UN anti-genocide envoy expresses alarm over reports of reprisal attacks by Malian troops, as France's Francois Hollande is due to visit Mali.

Russian President Vladimir Putin will lead tributes marking 70 years since the Battle of Stalingrad, seen as a turning point of World War II.

A quarter of a million Twitter users have had their accounts hacked in the latest of a string of high-profile internet security breaches.

France's President Francois Hollande says it would be wrong to assume the conflict in Mali is over after being given a rapturous welcome in Timbuktu.

Thirteen soldiers and 10 civilians have died in an attack by Taliban militants on a checkpoint in northwest Pakistan, officials say.