American warplanes shot down at least two and possibly four Iraqi fighter planes Wednesday that were attempting to flee to Iran, U.S. military officials said. Iraq announced it is severing diplomatic ties with the United States, Britain, France, Italy, Egypt and Saudi Arabia.

Warplanes from all of the countries except Egypt have taken part in the bombardment of Iraq and Kuwait that began on Jan. 17. Egypt has sent troops to join the multinational force but has not yet been involved in any combat.Brig. Gen. Richard Neal said two F-15 Echoes spotted two MiG-21s and two Su-25s that appeared to be headed to Iran.

"I can confirm that the two Su-25s were shot down," Neal said. "The two MiG-21s are listed as possible."

It was the first time Iraqi planes have been brought down by allied fire while fleeing to Iran for safekeeping. Neal, spokesman for the U.S. Central Command in Riyadh, Saudi Arabia, said 120 Iraqi planes are now on the ground in Iran, 95 of them fighter aircraft.

Neal also said that in the past 24 hours, 17 more Iraqis had defected or been taken prisoner, bringing the total number of POWs to about 850.

A Saudi spokesman, Col. Ahmed Al-Robayan said the allies have printed 25 million leaflets encouraging defections and dropped 14 million of them over Iraqi troop positions in Kuwait. Many of those surrendering carry the propaganda leaflets, he said.

Meanwhile, Iraq intensified its efforts to shoot down allied planes and claimed a major increase in deaths among its civilian citizens.

British Group Capt. Niall Irving said allied bombing had been curtailed by weather in the past 24 hours with some missions canceled altogether.

He said allied planes that did fly experienced "the heaviest air defense in some time," with one surface-to-air missile coming within a mile of a British Tornado.

Despite the barrage, there were no allied aircraft lost, he said. In Baghdad, the radio reported that 150 civilians, including 35 children, had been killed in overnight bombing raids in the southern city of Nassariyah. It was the highest number of civilian deaths reported in a single raid thus far.

Travelers arriving in Baghdad from Nassariyah reported the city came under intensive bombardment Tuesday night. They said military and industrial targets were hit.

Iraqi officials said the allied bombs and missiles raining down on Baghdad overnight smashed a hospital, bridge, communciations center and homes. Iraqi officials said two surface-to-surface rockets landed near a bus station, destroying two movie theaters and about 200 shops.

With prospects for a ground war heating up, allied commanders are determined to weaken the Iraqis' ability to fight back.

Gen. Norman Schwarzkof, commander of Operation Desert Storm, said his greatest concern in the war is that the Iraqis are "capable of the most heinous acts."

"They have demonstrated that they have absolutely no value on human life," Schwarzkopf said in a TV interview. "It's sort of the mad dog syndrome. In a mad dog there is no predictability."

In Washington, Secretary of State James Baker told Congress Wednesday that the task of ousting Iraq from Kuwait was "formidable" and that Saddam's regime was not a third-rate military power.

"Tough times lie ahead," Baker told the House Foreign Affairs Committee. "The military actions now under way necessarily involve many casualties" among both Iraqi civilians and allied forces.

The USS Missouri was in action overnight, firing its 16-inch guns at targets along the Kuwaiti coast, the command said. The battleship destroyed a radar site, artillery and a surface-to-air missile position. A dug-in Iraqi military unit also was hit, but the command said it didn't know how much damage was done.

One allied air raid scored a possible hit on an Iraqi mobile Scud missile launcher, the U.S. command said. The launchers have been used to lob missiles at Israel and Saudi Arabia, although the attacks have tapered off in recent days.

With half a million U.S. troops on land, sea and air in the gulf, President Bush is sending his top military men to the war zone to assess the 3-week-old campaign. Defense Secretary Dick Cheney and Gen. Colin Powell, chairman of the Joint Chiefs of Staff, will go to the gulf later this week.