US President Donald Trump waded into the European debate over migration as he dug in his heels over a controversial "zero-tolerance" immigration policy that has seen thousands of children forcibly separated from their parents at the Mexican border.

Trump pointed to Europe, which he said had become a "migrant camp," and said that would not happen to the US under his leadership.

Speaking at the White House, the US President said: "The United States will not be a migrant camp, and it will not be a refugee holding facility. You look at what's happening in Europe, and in other places, we cannot allow that to happen. Not on my watch."

He said criminals were using children like a "Trojan horse" to get into America, that "a country without borders is not a country at all," and that people coming in were bringing "death and destruction". He added: "They are thieves and murderers and so much else."

Criticising the more open immigration policies of his European Nato allies Trump wrote on Twitter: "Big mistake made all over Europe in allowing millions of people in who have so strongly and violently changed their culture!"

He specifically mentioned Angela Merkel, the German Chancellor, claiming "crime in Germany is way up" and immigration was why "the people of Germany are turning against their leadership".

Trump's claim on crime goes against crime figures in May that pointed to an overall decline in Germany over the past year. The figures showed that 5.76 million crimes were reported in 2017 - a drop of 5 per cent from 2016 and the lowest number since 1992.

Merkel's Bavarian allies yesterday gave her a two-week reprieve to set tougher border controls in the EU, saying that if she did not meet the deadline they would start rejecting asylum seekers at the German border.

The news came as the populist Italian Interior Minister Matteo Salvini pledged to start expelling Roma gypsies.

Following days of tense talks over the "migration master plan" of Horst Seehofer, the German Interior Minister, Merkel was given until an EU summit later this month to find a solution, also giving her time to consult other countries affected by the move such as Italy, Greece and Bulgaria.

Seehofer, leader of the CSU, which formed a coalition with Merkel's CDU party, said he wanted to shut the borders to all asylum seekers who have already been registered in other EU countries en route to Germany.

If the EU negotiations were to fail, Seehofer said he would go ahead with turning away asylum seekers at the German border as early as the first week of July.

Meanwhile, Salvini called for a census to be carried out of Roma gypsies in Italy, saying that he would expel any who did not have the legal right to be in the country.

As part of its election campaign, his party, the League, pledged to bulldoze illegal Roma camps. Many Roma people are Italian citizens who have been in the country for generations, while others come from Eastern Europe.