A series of heavy explosions shook Baghdad after sunset this evening as US forces stepped up their assault against insurgents in the Iraqi capital.
Earleir, two loud explosions echoed across the northern Iraqi city of Kirkuk this afternoon and plumes of smoke rose from two locations.
"These explosions you are hearing are a continuation of the 1st Armored Division's Operation Iron Hammer," a spokesman for US forces said, offering no further details.
A rapid series of deep booms shook the southern part of Baghdad in what sounded like a tank or armoured vehicle firing off rounds. Smoke could be seen rising from parts of the city.
US forces in Iraq have sharply stepped up military activity in the past 10 days, launching three major operations countrywide aimed at hitting a deepening guerrilla insurgency.
Operation Iron Hammer, which is focused in and around the capital, has also involved aerial bombardments of targets on the city outskirts and raids on neighbourhoods believed to harbour insurgents.
Around Saddam Hussein's hometown of Tikrit, 175 km (110miles) north of Baghdad, the 4th Infantry Division has launchedOperation Ivy Cyclone and Ivy Cyclone Two, dropping 500 lb (230kg) bombs on empty buildings, firing satellite-guided missilesand using tanks to attack suspected insurgent training camps.
Northern Iraq has been relatively peaceful since Saddam Hussein was toppled by US-led forces in April, unlike Baghdad and areas to its north and west that have been the scene of frequent violent attacks against occupying authorities, international organisations and Iraqis co-operating with them.