The US Senate has approved the construction of fencing along the southern border with Mexico.
The Senate backed a mixed series of measures
The move forms part of an immigration bill being discussed by senators, who also backed a plan to allow illegal migrants a chance at citizenship.
Hundreds of campaigners gathered in Washington to lobby senators.
Correspondents say the Senate vote largely follows the outlines of President Bush's speech on Monday, in which he proposed immigration reforms.
Mr Bush sought to appease both conservatives and pro-immigrant campaigners, proposing the creation of a "path to citizenship" for illegal incomers, along with steps to bolster border security.
On Wednesday, the Senate acted along similar lines, voting 83-16 to back the construction of 370 miles (595 km) of triple-layered fencing at strategic points of the southern border.
Fences 'cut crime'
"By passing my measure, we are sending a signal that we are serious about stopping the flow of illegal immigrants over the border," said the amendment's author, Senator Jeff Sessions.
US ILLEGAL IMMIGRANTS
About 11.5m illegal immigrants in the US
Four out of 10 have been in US five years or less
75% were born in Latin America
Most enter via southern US border
California, Texas and Florida host most illegal immigrants
Many work in agriculture, transport and construction
He said US regions where barriers already exist have experienced lower crime and a stimulated economy.
Opponents of fences say they increase deaths among desperate would-be immigrants, who must travel to more remote areas to try to cross.
The measure also calls for the installation of vehicle barriers on a 500-mile stretch of the 2,000-mile border.
By 66-33 votes, the Senate threw out a proposal that would have removed provisions allowing illegal immigrants the chance to gain citizenship - although it blocked illegal immigrants with criminal records from becoming citizens.
Senators also approved the creation of a guest-worker programme similar to that put forward in President Bush's Monday speech.
Wrangles to come
Immigration reform activists from more than 20 states tramped the corridors of the elegant Senate building all day, reported news agency AFP, lobbying senators ahead of the vote.
Up to 1,000 demonstrators later gathered on Washington's National Mall, to emphasise the value of immigrants to the United States.
The final shape of immigration legislation is not yet definite, as the Senate proposals must be reconciled with measures backed by the House of Representatives.
The House has approved a much tougher bill, which makes illegal entry a crime, gives illegal immigrants no options to become citizens, and proposes the construction of fencing twice as long as that backed by the Senate.
There are reported to be about 11.5 million illegal immigrants in the United States, and each year some 500,000 to a million more enter the country, mostly via the border with Mexico.
US-MEXICO - HOUSE PROPOSAL
Representatives want 1,130km (700 mile) barrier along part of border
Border guards made 1m arrests in 2005
500 people died trying to cross illegally in 2005, say rights groups
Thousands cross legally daily to shop and work - in 2003 88m cars, 48m pedestrians crossed