GENEVA: Detaining migrants should be a last resort, the United Nations said on Friday, after US President Donald Trump unveiled a surprise plan to detain thousands of undocumented migrants in Guantanamo Bay.

On Wednesday, Trump said he had ordered the construction of a detention camp to hold up to 30,000 of what he called `criminal illegal aliens` at the notorious US military facility on the eastern tip of Cuba, used for holding terrorism suspects since the Sept 11, 2001 attacks on the United States.

`It is essential to uphold the dignity and rights of all individuals, regardless of their immigration status, and to ensure they are treated in accordance with international human rights standards,` UN human rights office spokesman Jeremy Laurence told reporters in Geneva, when asked about the plans.

`Detention of migrants should be used as a last resort. And only in exceptional circumstances.` He added: `Regardless of their status, migrants have human rights and they should be respected, wherever.` Trump`s plan intensifies the crackdown on illegal immigration that he has pledged in his second term.

`We have 30,000 beds in Guantanamo to detain the worst criminal illegal aliens threatening the American people,` he said at the White House, adding that it would `double our capacity immediately` to hold undocumented migrants.

The Guantanamo Bay facility currently holds 15 detainees from the wars in Afghanistan, Iraq and other operations triggered by the Sept 11, 2001, attacks.-AFP