Updated

The top U.S. commander in Afghanistan, Gen. Joseph Dunford, is warning his troops to be ready for increased violence because of a series of anti-American statements by Afghan President Hamid Karzai.

Karzai has accused the U.S. of colluding on suicide attacks with the Taliban to keep the country unstable and give foreign forces an excuse to stay beyond their 2014 mandate.

Dunford emailed his commanders on Wednesday, as first reported by The New York Times.

A senior U.S. military official confirmed Thursday that the email is genuine. The official spoke on condition of anonymity in order to discuss the private communication.

Dunford also says unusually warm weather could mean an early start to the Taliban fighting season because militants can return from now-open high mountain passes from Pakistan.