It was still not clear where the 400 troops would be drawn from or once chosen where they would be based, although Qatar, Saudi Arabia or Turkey have said they would host them.
The U.S. has a goal of training over 5,000 rebels each year for the next three years.
This marks an increase in training by the U.S. of Syrian rebels. This training started in Jordan back in March of 2013.
The covert program has the CIA as the lead. In October of 2014, an announcement was made that said the project would be increased and a parallel program from the Pentagon would be set up.
This latest announcement comes only days after U.S. senior officials met with opposition leader from Syria in Turkey.
The U.S. is hoping that the training of the rebels will turn out more effective fighting the militants from IS.
Across the Syria border in Iraq, the United States has sent over 3,000 troops that are training Kurdish and Iraqi forces.
Critics of that training mission have said it is not large enough and has been too slow to have an effect against the radical militant group.
The CIA said it estimates that the Islamic State could have up to or more than 31,500 fighters.
There also are concerns that the U.S. could end up training these rebels that could be linked to other groups that are radical and extremists such as Nusra Front an affiliate of al-Qaeda.
The U.S. has continued to carrying out with coalition members, air strikes against the Islamic State inside both Syria and Iraq since August in an attempt to both degrade as well as destroy the militant group.