Citizenship question in US Will Leave no Stone Unturned- President Trump

Instead, he said he had directed officials to obtain the information through an executive order for government agencies, as court challenges would have delayed a census.

"We will leave no stone unturned," Trump said.

The retreat follows a long fight over the inclusion of the question, which the Supreme Court had blocked in June.

"We are not backing down on our effort to determine the citizenship status of the United States population," the US president said.

The order will require government agencies to hand over documents regarding citizenship.

"As a result of today's executive order we will be able to ensure the 2020 census generates an accurate count of how many citizens, non-citizens and illegal aliens are in the United States of America," Mr Trump said at the White House.

Kristen Clarke, president of the National Lawyers' Committee for Civil Rights Under Law, told the BBC she had concerns about Mr Trump's plans.

"This is essentially an attempt to compile data on a mass scale in a way that is unprecedented," she said. "We don't know how long it will take for them to pull this data together, we don't know what they will do with that data."

What reason did the Trump administration give?

The decision to abandon the citizenship question was a "logistical impediment, not a legal one", said Attorney General William Barr, standing alongside President Trump.

He said there was "ample justification" for the administration to include the citizenship question.

But referring to court injunctions, he said there was no way to "implement any new decision without jeopardizing our ability to carry out the census".

Census questionnaires without the citizenship question are already being printed.

Mr Barr repeatedly congratulated Mr Trump on the executive order.

How did the battle unfold?

At the end of last month, the Supreme Court returned the case to the Census Bureau in a 5-4 ruling that noted the reason for including the question seemed "contrived".

Government lawyers indicated they had dropped the question and officials began printing the 2020 census without it.

But Mr Trump then announced that he might consider an executive order to include the question or find other ways to move forward.

Legal experts noted that an executive order could not override a Supreme Court ruling.

In election year, a question about citizenship on the 2020 census form would have been hugely polarizing.

For Donald Trump, whose stance on illegal immigration has defined his presidency, it would have been a major success.

But it is not to be. The hurdles proved too cumbersome and the administration acknowledged that outstanding lawsuits could delay the completion of the census.

But never one to admit defeat, Mr Trump framed his plan B as a "far more accurate" way to count the non-citizen population. Officials, he said, would "leave no stone unturned", in their quest to dig out citizenship information from existing data held by government departments.

That could be seen as an implied threat, but it means the census is likely to result in a more accurate count, with those living in the US illegally less afraid to make their presence known.

Census counts are used to determine the allocation of seats in the House of Representatives and the distribution of billions of dollars of funds in federal spending.

There had been concern that impoverished areas would lose out if a significant number of residents chose not to complete the form.

The citizenship question has not appeared on a US census for all Americans since 1950, though it has been put to some subsets of the population between 1970 and 2000.