'Berlin Wall'

But the costly plan may be stalled by insufficient funds despite the $1.2bn previously approved by the US congress.

"Geography has made our countries neighbours, but the choice we've made for each other is a choice for freedom. And that choice has made us friend"

George Bush, US president

Last month, Michael Chertoff, the homeland security secretary, said construction of the entire stretch may not be necessary.

Calderon had ridiculed the proposed fence, a mix of physical and high-tech barriers, and likened it to the Berlin Wall, arguing that it would do little to stem illegal migration.

At the same time, he acknowledged Bush's immigration reforms aimed at improving economic conditions and generating more jobs in Mexico as "the only way in order to truly solve the migratory issue".

Bush is not getting his Republican party's support on immigration reforms including a guest worker programme and a naturalisation exercise for some of the 12 million undocumented workers already in the country.

"In the debate on migration, I remind my fellow citizens that family values do not stop at the Rio Grande River, that there are decent, hardworking honourable citizens of Mexico who want to make a living for their families," Bush said.

"And so, Mr President, my pledge to you and your government, but, more importantly, the people of Mexico, is I will work as hard as I possibly can to pass comprehensive immigration reform," he added.

Drug demand

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In welcoming Bush to the Yucatan Peninsula, Calderon said the continued high demand in the US made it hard to reduce Mexico's drug production.

"We need the collaboration and the active participation of our neighbour," he said.

He said it was time for a fresh start to "direct our relationship toward a path of mutual prosperity".

Bush said: "Geography has made our countries neighbours, but the choice we've made for each other is a choice for freedom. And that choice has made us friend."