US strategy against ISIS will include air strikes, training of security forces

US President Barack Obama has authorised air strikes against Islamic State group targets inside Syria for the first time, pledging to destroy its fighters "wherever they exist".

In an address yesterday, Obama also announced an expansion of strikes in Iraq, saying he would be dispatching nearly 500 more US troops to the country to assist its besieged security forces.

Saudi Arabia, a crucial US ally in the Middle East, offered to host the training missions, part of Obama's effort to persuade other nations to join with the US in confronting the self-declared jihadist fighters.

"This is not our fight alone," Obama declared.

"American power can make a decisive difference, but we cannot do for Iraqis what they must do for themselves, nor can we take the place of Arab partners in securing their region."

"Our objective is clear: We will degrade and ultimately destroy ISIL (Islamic State) through a comprehensive and sustained air strikes strategy.''

Obama adamantly ruled out the prospect of putting American troops in combat roles on the ground in Iraq or Syria, calling on Congress to authorise a programme to train and arm rebels in Syria who are fighting both the Islamic State group and Syrian President Bashar Assad.