American troops could be in Iraq for years and can expect heavy casualties in the next few months as they struggle to wrest the initiative from insurgent groups, a senior US officer said yesterday.

The warning came on a day when 25 people were killed near Ramadi in two suicide bombings police blamed on al Qaeda. They were the latest in a string of big car bombings across Iraq in recent weeks that have killed hundreds despite a US-backed security crackdown in Baghdad and outlying areas.

Major-General Rick Lynch, who commands US forces south of Baghdad, said the lesson of recent history was that it took an average of nine years to overcome internal uprisings and that there was "no instantaneous solution" to Iraq.

He added the military was bracing itself for a spike in the numbers of troops killed and wounded from now until September as US reinforcements moved in to stabilise hardline areas of the Iraqi capital.

"All of us believe that in the next 90 days or so you'll probably see an increase in American casualties because we are taking the fight to the enemy. This is the only way we can win," he said.

His remarks follow a weekend in which 12 US soldiers were killed, eight in roadside bomb attacks on Sunday. General Lynch's Task Force Marne has sustained 13 dead and 39 wounded since April 1.

He also said his troops were increasingly being targeted by the sophisticated, shaped-charge explosive penetrators which coalition commanders claim are smuggled from Iran and which are powerful enough to defeat even tank armour.

An increasingly "thinking enemy" had also learned to counter hi-tech detection devices by burying bombs deeply and compensating for the reduced blast by making them bigger.

"The enemy dominates the terrain. He has the opportunity to set traps and ambushes. As soon as we do something to prove our capability, he does something to defeat it," General Lynch said.

While he predicted that new tactics of planting small garrisons in the heart of areas formerly controlled by militias in the capital would have a decisive effect on insurgents by the end of this yearm he was less optimistic about political progress.

"You can't just build a government overnight. I can't see significant advances in that sphere in the same timeframe. Bringing stability to Iraq could take years."

The general's warning about more casualties was repeated by White House spokesman Tony Snow "We are getting to the point now with the Baghdad security plan where there is going to be real engagement in tougher neighborhoods and you're likely to see escalating levels of casualties," he said.