He said the US military had not yet completed a plan for how to accelerate the training and equipping of Baghdad's forces.
"When a finalised plan is presented to me by the Pentagon, then I will share it with the American people. We don't yet have a complete strategy because it requires commitments on the part of the Iraqis as well about how recruitment takes place."
His comments come ahead of the first anniversary of Isis' declaration of a caliphate. On June 29 last year, the group announced Abu Bakr al Baghdadi as its leader, or caliph.
In the past 12 months the group has shown a brutality that has shocked the world but has also managed to attract recruits through a sophisticated use of social media.
It has also proven to be a difficult force to defeat.
In the past year, the US and a coalition of allies have launched more than 4000 airstrikes in Iraq and Syria but have been unable to prevent key cities falling to the jihadists.
Kurdish fighters have been among the most successful on the ground, defeating Isis in a long battle for the Syrian town of Kobane near the Turkish border.
Obama insisted that Iraqi forces "operate effectively" where they have been trained and equipped by the US. The US has trained around 7000 Iraqi soldiers in a series of six-week training camps but none of those 7000 were deployed in unsuccessful effort to defend Ramadi.
There are around 3000 American troops currently deployed in Iraq.
New Zealand has 143 troops in Iraq to help train Iraqi troops.