The United States is expected to announce on Wednesday plans for a new military base in Iraq's Anbar province and the deployment of around 400 additional U.S. trainers to help Iraqi forces in the fight against Islamic State, a U.S. official said.

The plan would expand the 3,100-strong U.S. contingent of trainers and advisers in Iraq and would mark an adjustment in strategy for President Barack Obama, who is facing mounting criticism for not being tougher in combating Islamic State.

U.S. officials, speaking on condition of anonymity, expressed hope that even a modestly strengthened U.S. presence could help Iraqi forces plan and carry out a counter-attack to retake Anbar's capital Ramadi, which insurgents seized last month.