American troops are closing in on the Iraqi capital Baghdad, knocking out two divisions of Saddam Hussein's Republican Guard as they continue battles with the country's best trained troops. U.S. forces have now advanced to within some 30 kilometers of the Iraqi capital, where reports say they are again exchanging more heavy fire with Republican Guard Units.

Pushing through the towns of Al-Kut and Karbala, U.S. forces are closing in on Baghdad in a multi-pronged approach, virtually wiping out two Republican Guard divisions, some units destroyed, others surrendering, but all no longer able mount a defense of the capital.

"It's clearly threatening Baghdad and threatening the core of the regime," U.S. General Stanley McChrystal.

The Pentagon says coalition forces continue to face resistance despite questions about Saddam Hussein's grip on power.

U.S. military officials say an Army Black Hawk helicopter has been shot down near Karbala, but there are conflicting reports of casualties. And, reports are also coming in of new artillery battles between Republican Guard divisions heading south and advancing on coalition forces.

"We are expecting or at least planning for a very difficult fight ahead. We are not expecting to drive into Baghdad suddenly and seize it," said General McChrystal.

U.S. Marines have now moved past the so-called 'red zone', an imaginary circle on the map ringing Baghdad, where, once crossed, allied commanders fear Iraq could unleash chemical or biological weapons as a final line of defense.

Defense Secretary Donald Rumsfeld says U.S. intelligence is detecting signs that Iraq may be preparing to use them. "We keep seeing chatter in the intelligence channels about the possibility. We've discovered caches of chemical protective gear that the Iraqis have stored," he said.

And, in another sign that the Iraqi government is growing increasingly nervous, state television Wednesday called on Iraqis to turn in their mobile phones, saying it believed some people are using them to collaborate with the enemy. The Pentagon has said U.S. military commanders have been contacting top Iraqi commanders by mobile phone and e-mail for weeks.

President Saddam Hussein was again seen on Iraqi television, meeting with his top military advisers. But there was no way to determine from the broadcast when the meeting actually occurred. It was left to his information minister Mohammed al-Sahaf to deny the allies' reported advances.

"They are lying always and mainly they are lying to their public opinion. Therefore what they have alleged about a breakthrough, this is completely an illusion," he said.

In Baghdad, correspondents report a coalition air strike Wednesday damaged a Red Crescent maternity hospital and other civilian buildings, causing a number of casualties. U.S. Central Command in Qatar says it is reviewing targeting information to determine whether the facility may have been damaged by a missile that could have landed nearby.