FACTBOX - Piracy on the high seas

(Reuters) - Pirates have seized a Saudi-owned oil supertanker off east Africa, the U.S. Navy said on Monday.

Piracy has been growing for several years off the Horn of Africa, and near-daily attacks are now forcing many shippers to seek alternative routes.

The hijackers demand big ransoms from ship owners, threaten humanitarian supplies and push insurance costs sky-high.

Here are some details:

* INCIDENTS IN THE LAST WEEK:

-- The Sirius Star, with 25 crew from Croatia, Britain, the Philippines, Poland and Saudi Arabia, was attacked 450 nautical miles southeast of Mombasa, Kenya, the U.S. Navy said on Monday. It is the first tanker to have been seized in the area. The vessel can carry up to two million barrels of crude oil.

-- A Russian navy patrol boat scared off pirates who tried to capture the Saudi Arabian merchant ship Rabih in the Gulf of Aden on Sunday, the Russian navy told Interfax.

-- On Saturday, a Japanese cargo ship was reported seized by pirates off Somalia. It was carrying 23 sailors, including five South Koreans, Yonhap said.

-- A Chinese fishing boat was reported seized off the Kenyan coast late on Thursday. The crew included 15 Chinese, one Taiwanese, one Japanese, three Filipinos and four Vietnamese.