The U.S. Senate has approved a bill to build a 1,100-kilometer fence along parts of the 3,200-kilometer border with Mexico to prevent illegal immigration.

Senators overwhelmingly passed the legislation by a vote of 80-19 late Friday as they prepared to head to their home states to campaign for upcoming congressional elections.

The House of Representatives passed a border fence bill earlier this month.

President Bush is expected to sign the bill into law, even though the legislation does not include other reforms, including the guest worker program he wanted, and provisions to eventually offer citizenship to some 11 million illegal immigrants already in the country.

Critics call the proposed law "election-year politics," and say it ignores the need for broader immigration reform.

Proponents of the fence bill say it will help to prevent illegal immigrants, criminals and terrorists from sneaking into the United States.

Mexico strongly opposes the building of a border fence. Mexican Foreign Secretary Luis Ernesto Derbez said late Friday Mexico will send a letter to President Bush explaining why it thinks a barrier along the common border is not the right solution.

Border security and illegal immigration are major campaign issues in the U.S. legislative elections on November 7.

Some information for this report provided by AP, AFP and Reuters.