Hundreds of thousands of people have protested across the US against plans to tighten the law on immigration.

Rally organisers described the protest movement as "the fight for civil rights of our generation".

Unions, civil rights groups, schools and churches oppose a bill in Congress, which would make illegal immigration a full criminal offence.

The protesters want Congress to approve a provision allowing undocumented workers to remain in the country.

They also oppose plans to construct extra security fencing on the Mexican border.

On Friday, the US Senate failed to reach agreement on a compromise deal that would allow an estimated 11.5 million illegal immigrants apply for US citizenship.

President George W Bush backs the guest-worker scheme but faces stiff opposition within his Republican party.

The Senate will resume the debate on the issue in two weeks' time, after the spring recess.

The measures agreed by senators will then have to reconciled with a tough bill passed by the House of Representatives in December.

Many of the protests in recent weeks have been directed at the House bill.

'Better life'

Demonstrations were held in up to 100 cities and towns - including Chicago, Los Angeles, Las Vegas and New York, where organisers claimed 100,000 people had turned out.

In Los Angeles, home to a large Hispanic population, some 5,000 people held a candlelit vigil.

In Atlanta, protesters brandished banners declaring "We have a dream", invoking civil rights leader Martin Luther King.

One protester among the 30,000 there, Mexican immigrant Carlos Carrera, said: "We would like them to let us work with dignity. We want to progress along with this country."

He carried a banner reading: "We are not criminals. Give us a chance for a better life."

Senator Edward Kennedy echoed the Martin Luther King allegory when he addressed thousands in Washington.

"It is time for Americans to lift their voices once again - this time in pride for our immigrant past and in support of our immigrant future," he said.

Many protesters in the capital bore banners reading "We are America" and wore white T-shirts symbolising peaceful protest.

One protester, Carol Vega, said: "Last time I read the Bible, there was no requirement to be checking passports."

Election issue

Police in Phoenix, Arizona, said a rally of 50,000 people stretched a mile long.

Eliseo Medina, an organiser of the New York rally, said: "We march in the streets, but we will also march to the voting booth in November."

The immigration issue is set to become a key one in the mid-term elections, with Latinos the nation's fastest-growing voting bloc.

The BBC's Americas editor, Simon Watts, says the millions of illegal immigrants are starting to form a major political movement.

But, he says, it is still in its early stages. No national leader has emerged and efforts to turn grassroots pressure into an organised voting bloc are just starting.

"The reason why they don't listen to many migrants is because they cannot vote. But hopefully that will change," Roland Roebuck, 58, a half-Puerto Rican man in Washington DC told the Reuters agency.

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