Fierce sandstorms have been holding up US-led forces in their advance towards the Iraqi capital, Baghdad.
Troops have had to sit and wait for the storms to clear
BBC correspondents travelling with coalition troops say units have been halted, with visibility reduced to just a few metres.
However, the weather has not prevented US B-52 aircraft from dropping huge payloads of bombs south of the capital.
The air strikes are targeting the Medina division of the elite Republican Guards, digging in for what both sides agree will probably be a decisive encounter, says the BBC's Paul Wood.
The chairman of the US joint chiefs of staff, General Richard Myers, acknowledged that bad weather was slowing down the advance, but vowed that it would not be stopped.
Major-General Victor Renuart of US Central Command said 1,400 air sorties against the Iraqi Republican Guard were scheduled for Tuesday.
Iraq's Information Minister Mohammed Saeed al-Sahaf said 16 people had been killed and 95 wounded in Baghdad in the previous 24 hours.
Command Sergeant Major Kenneth Preston - who oversees the Third Infantry Division - told the Associated Press news agency that about 500 Iraqis had been killed in the past two days by American infantry, tanks and mechanised units sweeping through the south of the country.
The BBC's Gavin Hewitt - who is about 160 kilometres (100 miles) south of Baghdad - says all operations have ceased as a result of the storm.
Rivulets of sand are flowing across the desert floor and everybody is hunkering down, he says.
However, at coalition headquarters in Doha, Qatar, a US spokesman said military activity was continuing with all-weather precision weapons.
And in Washington, General Myers vowed to press on, regardless of the weather.
But the coalition has been forced to call back some combat missions from aircraft carriers in the region, according to the Associated Press.
A dozen aircraft were launched from the USS Harry Truman in the Mediterranean on Tuesday on two strikes but returned to the carrier a few hours later without reaching northern Iraq.
Strike pilots from the USS Kitty Hawk in the Gulf switched to satellite-guided weapons for strikes.
Captain Patrick Driscoll, commander of the air wing aboard the USS Kitty Hawk, said the weather would "affect our package a little bit, but not our ability to support the battlefield".
Lieutenant Colonel Laura Richardson, a Black Hawk pilot who commands the 101st Airborne
Division's 5th Battalion said the sandstorms were very frustrating.
"These things can come in so fast," he said.
General Myers said the coalition anticipated that "as we get closer to Baghdad, the resistance will get tougher".
"That's where their best units are, the so-called Republican Guard units. They're the best trained, best equipped and reportedly the most loyal to the regime, so we think the toughest fighting is ahead of us... and we're preparing for that," General Myers told ABC television.
The approaches to Baghdad are flat, but there are also villages, small towns, orchards and crops, which could provide plenty of cover for Iraqi troops.
The Iraqi authorities say the US-led forces will be in for a surprise when they reach cities, our correspondent there says.