U.S. President Barack Obama and other NATO leaders have begun the second day of a summit meeting in Warsaw that's expected to lead to decisions about Afghanistan, the central Mediterranean and Iraq.

On Friday, leaders approved the deployment of four multinational NATO battalions to Poland and the Baltic states to deter Russia, as well as a Romanian-Bulgarian brigade for the Black Sea region.

The Warsaw summit, NATO's first in two years, is considered by many to be the alliance's most important since the Cold War.

NATO Secretary-General Jens Stoltenberg says NATO needs to adapt to confront an array of new threats to its member nations' security, including cyberattacks and violent extremism generated by radical Muslim organizations like the Islamic State group.