Trump sacks US Homeland Security secretary Kirstjen Nielsen over illegal migration - report

US President Donald Trump has sacked Department of Homeland Security (DHS) Secretary Kirstjen Nielsen over illegal migration from the southern border, according to reports.

Trump said on Twitter Kevin McAleenan, the current US Customs and Border Protection commissioner, would become the acting DHS secretary.

"Secretary of Homeland Security Kirstjen Nielsen will be leaving her position, and I would like to thank her for her service," Trump said.

"I am pleased to announce that Kevin McAleenan, the current US Customs and Border Protection Commissioner, will become Acting Secretary for @DHSgov. I have confidence that Kevin will do a great job!"

The Washington Post reports Trump blamed Nielsen for growing illegal immigration at the United States' southern border with Mexico.

AP reports Nielsen met Trump at the White House on Monday (NZ time) after the pair went on a trip to the border last week.

She had been frustrated at other departments' resistance to helping with the growing number of families crossing the border illegally.

Trump has threatened to fire her before, but at the time there was no suitable successor in place.

Nielsen, 46, had held the position since December 2017.

She led a sprawling department responsible for carrying out some of Trump's most contentious policies, such as his plan to build a wall on the border with Mexico and the separation of migrant children from their families.