Attackers blew up a power transformer with a rocket-propelled grenade, injuring two U.S. soldiers and sending a tower of flame into the night sky over the city of Fallujah, witnesses and the U.S. military said Friday.

It was the latest of a spiraling series of attacks on U.S. soldiers and sabotage against the infrastructure needed for Iraq's reconstruction.

The U.S. military said one of the suffered a concussion and the bruises from the impact of the rockets exploding near two Bradley fighting vehicles at the gate.

The soldiers returned a barrage of gunfire into the darkness, said Soadad Khalil, the supervisor on duty at the power plant in Fallujah, 35 miles from Baghdad.

However, Capt. James Brownlee of the 3rd Infantry Division said there was no firefight. More troops rushed to the area and rounded up 40 Iraqis trying to flee. He did not say how many remained in custody Friday.

The attack knocked out one of the two transformers at the power plant, which provides nearly half the electricity to this city of about 75,000 people. Fallujah has been a center of resistance to the coalition occupation of Iraq.

Brownlee said the attack was directed against the troops on guard at the facility, but the rockets missed their targets. The transformer was still smoldering more than 12 hours after the attack, which happened shortly before midnight.

Khalil said the station's employees were assessing the damage to see what could be salvaged.

Sabotage against power and water installations has been a key element of the anti-American resistance, which has been growing in recent days despite U.S. officials insistence that it is not being organized centrally.

Despite efforts to increase electricity generation, the U.N. Development Program reported Thursday that power delivery to Baghdad fell to 800 megawatts from 1300 megawatts two weeks ago. It attributed the fall to the sabotage of power lines and breakdowns caused by daytime temperatures reaching 113 degrees Fahrenheit.

Daily attacks against the U.S.-led coalition have grown increasingly lethal in the last week. On Thursday, assailants fired a rocket-propelled grenade at a military ambulance south of Baghdad, killing one American and wounding two others. He was the third soldier to die from hostile fire this week alone.

Two men fired an rocket-propelled grenade at a tank late Wednesday in Samarra north of the capital, causing little damage and no casualties. One attacker was killed and the second captured.

Attackers also fired a rocket-propelled grenade at a U.S. tank north of Baghdad, and a U.S. Army truck was set on fire in the western part of the capital. The military reported that three mortar shells hit outside a coalition-run aid office in the town of Samarra on Tuesday, killing one Iraqi and wounding 12.

The guerrilla-style attacks came as U.S. forces conducted house-to-house searches for weapons and arrested hundreds of people across Iraq.