Country singer Trace Adkins performs the "Marine Song" with US Marine Corps Band during a full-dress rehearsal

Americans are celebrating the Memorial Day weekend - the unofficial start of summer in the United States.

The holiday was originally intended to honor soldiers who died in the American Civil War more than 140 years ago, but it has become a three-day weekend of parades and other ceremonies to honor all U.S. military personnel killed in battle, including the ongoing operations in Iraq and Afghanistan.

On Saturday, President Bush used his weekly radio address to salute those, who made the ultimate sacrifice. On Monday, the official holiday, the president will visit Arlington National Cemetery near Washington where more than 260,000 military veterans are buried.

The first summer holiday is also used by tens of millions of Americans for travel. Airports have been crowded with passengers, and highways are busier this year, despite increased gasoline prices.