The Army general who ended his tenure this month as the top U.S. commander in Afghanistan says this may be a particularly difficult year for Afghan security forces fighting the Taliban.

Gen. John Campbell said Friday that the Afghans need to follow through with promised changes, such as taking a more aggressive, offensive approach on the battlefield.

The Afghan forces took heavy losses last year, which was their first full year of fighting without U.S. troops in combat alongside them.

Campbell gave up command of Operation Resolute Support, as the U.S. mission in Afghanistan is known, in March and is due to retire from the Army on May 1.