Updated

The United States is preparing for attacks by Hezbollah militants on Americans during a planned evacuation out of war-torn southern Lebanon early Wednesday, military officials said.

"I’m concerned about attacks on ships. We do not assume anything. And that sort of scenario is something we are planning for," Vice Admiral Patrick Walsh told reporters Tuesday.

The United States is working with Israel through European Command, its segment of U.S. forces, to coordinate the evacuation of up to 5,000 Americans from war-torn Lebanon once a chartered Greek cruise ship gets into port, Walsh said.

At least 320 Americans were evacuated from Lebanon to Cyprus by the end of Tuesday and that 1,000 more will leave the following day after the Greek cruise ship arrived at port.

The State Department said 5,000 Americans trapped in the war-torn region of Lebanon had requested to be evacuated and a fleet of vehicles was en route to the area to ship out Americans.

The Orient Queen time, left the Mediterranean island of Cyprus for Beirut, to join several U.S. military helicopters already ferrying dozens of Americans out of southern Lebanon.

“The threat level allows us to move ferries back and forth but it's not something we take for granted. We'll also have warships in position to ensure the safe passage of citizens from Lebanon to Cyprus,” Walsh said.

The Navy dispatched the destroyer USS Gonzalez to Beirut to escort the Orient Queen out of the embattled port city.

The USS Iwo Jima, which carries helicopters and jump jets, was deployed Tuesday morning, should arrive with 2,000 Marines to assist in evacuations by the end of the week.

The 24th Marine Expeditionary Unit, on exercises in the Red Sea, has been ordered to waters off Lebanon to help in the evacuation. By day's end, the U.S. military will have six CH-53 Super Stallion helicopters available to move 300 passengers a day out of Lebanon. Other U.S. ships should arrive in a day or so.

The Hual Transporter, a ship chartered by Sweden, left Beirut Tuesday evening with 1,000 Scandinavians and other Europeans, and Feltman said 200 Americans also were aboard. Other Europeans were able to depart Lebanon by plane.

U.S Ambassador Jeffrey D. Feltman told The Associated Press that by the end of the week the evacuation would be proceeding at a pace of 1,000 Americans a day, and defended the process in the face of Americans' complains that it took to long to start moving them out.

"We at the Embassy don't have the experience to move a lot of people. Luckily, the U.S. government does," he said. A team of U.S. security experts arrived in Lebanon over the weekend to plan the evacuation.

On Tuesday, U.S. military helicopters were ferrying 120 Americans to Cyprus — half of whom had already been flown out. The other 200 Tuesday were boarding a Swedish-chartered ship in Beirut's port that was taking hundreds of Europeans,

He said 1,000 more Americans would leave on Wednesday, going by sea.

"A thousand a day will be leaving by the end of the week," he said, without elaborating. He did not say how many ships would be involved in the evacuation.

At the U.S. Embassy in the northern edges of Beirut, the final group of 60 Americans going out helicopter Tuesday waited for their turn to leave, their backage piled on a helicopter pad. Around 20 Marines in camoflage stood nearby.

The embassy put out a statement advising other Americans to "not move" from their homes until it informed them it was time to go. "All Americans who wish to be transported, although not everyone will travel at the same time," it said in a statement.

The U.S. has sent a cruise ship, "The Orient Queen," capable of carrying 750 passengers to help in the evacuation. It left Cyprus in the morning and the embassy said earlier it would start the evacuation Tuesday, but just before nightfall it had still not arrived at Beirut's port. The ambassador's comments suggested it would be used Wednesday. Officials were not likely to try moving hundreds of Americans through the city to the port after nightfall.

Another ship, the Hual Transporter, chartered by Sweden was in the port Tuesday afternoon loading up to 1,000 Scandinavians, other Europeans and around 200 Americans — mostly students.

U.S. military helicopters ferried out 21 Americans on Sunday, followed by 100 more on Monday, most of them ill or needing to leave quickly for humanitarian reasons.

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FOX News' James Rosen and Cassie Carothers and the Associated Press contributed to this report.