victory over insurgents in Afghanistan would not be "quick" nor "easy".

PHOENIX :US President Barack Obama warned Monday that victory over insurgents in Afghanistan would not be "quick" nor "easy".

"The insurgency in Afghanistan didn't just happen overnight," Obama told the Veterans of Foreign Wars service organization in the South-western state of Arizona, ahead of Afghanistan's presidential election August 20.

"We won't defeat it overnight. This will not be quick, nor easy," Obama said, as he explained his new strategy of intensifying the fight against the Taliban and Al-Qaeda in Afghanistan and Pakistan now taking effect.

The president defended the war as a necessary conflict, which was "fundamental" to the defense of American people in depriving Al-Qaeda of a safe-haven to plot follow on attacks to the September 11 strikes in 2001.

Obama noted an upsurge in "fierce" fighting in Afghanistan, but vowed to constantly adapt US tactics and offer the troops the tools and equipment, they need.

Obama has already ordered an additional 21,000 troops to Afghanistan ahead of Thursday's elections, in line with his strategy of turning the US focus from Iraq to a conflict, he says poses a greater security threat.