A flotilla of U.S. warships carrying as many as 8,000 American sailors heading for a four-day Thanksgiving holiday visit to China's port of Hong Kong has been refused entry, the U.S. Navy said Thursday.

It was not immediately clear why the USS Kitty Hawk aircraft carrier and its support vessels were barred Wednesday. Port officials said they had not been notified of the previously scheduled visit. But the incident added an unusual twist to China-U.S. relations, strained in recent months by disputes over trade and Iran's nuclear program.

In the past, China has banned all U.S. ships from the former British colony during times of tense relations. But current relations are not too bad, said David Zweig, a professor of China relations at the Hong Kong University of Science and Technology said.

"This is a surprise," Zweig said. "I haven't heard of ships being turned away like this before. I'm also disappointed and saddened for the families who have flown here expecting to see their relatives and are not now going to have their reunions."

The Kitty Hawk and five support vessels including a nuclear fast attack submarine were expected to dock in Hong Kong's deep water port Wednesday morning.

But the group was refused entry, Lt. Cmdr. Amy Derrick-Frost told The Associated Press by telephone from the U.S. Navy's Pacific Command headquarters in Hawaii.

"There is no information as to why they were not allowed to pull into the port for the scheduled visit," she said.

The group of vessels were on their way to home ports, she said.

Hong Kong has long been a favored port of call for the U.S. military but Beijing's approval has been required since July 1, 1997, when Britain handed this former colony back to China.

Hong Kong's Marine Department, which handles logistic arrangements for ships docking in Hong Kong's deep-water port, said Thursday it had not received the documentation it normally would receive from other agencies clearing the arrival of foreign military ships.

The Hong Kong office of China's Ministry of Foreign Affairs said it would look into what happened.

China banned U.S. ships entering Hong Kong waters in 1999 when NATO planes bombed the Chinese embassy in Belgrade during the Kosovo crisis and refused port calls for several months after a U.S. spy plane collided with a Chinese fighter jet in April, 2001.

Plans for many of the sailors to spend Thanksgiving with American families living in Hong Kong have had to be canceled, said Shirlee Algire, a volunteer who organizes the home meals. Some 47 families had offered to host 202 sailors on Thursday, Friday and Saturday, Algire told the AP.

The 46-year-old Kitty Hawk, which is based in the Japanese port city of Yokosuka, is the only U.S. aircraft carrier permanently deployed abroad.

The diesel-powered ship will be decommissioned next year and replaced by the nuclear-powered USS George Washington.

Relations between China and the United States have improved in recent years, but the two powers are at odds over how to resolve Iran's failure to halt enrichment of uranium and the growing trade deficit in the U.S.