Democratic Republic of Congo has summoned the Angolan ambassador over the expulsion of thousands of Congolese migrants from Angola during a crackdown on artisanal diamond mining this month, Congo's foreign minister said on Wednesday.

"Angola [should] conduct a comprehensive investigation to establish who is responsible for these wrongful acts," Foreign Minister Leonard She Okitundu said in a statement.

Congolese fleeing Angola, estimated to be 28,000 by the DR Congo government, said they had been forced to leave by Angola.

Some of them accused the Angolan police of carrying out human rights abuses.

In a speech on Tuesday to parliament, Angola's President, Joao Lourenco, said illegal immigration linked to illicit diamond mining had reached alarming levels.

In order to be less reliant on oil the mining sector is to be reformed and President Lourenco said the days when anyone could join in the hunt for diamonds were now over.

Angolan Police Commissioner Antonio Bernardo denied the accusations of violence on Wednesday, and said that the border agreement between the two countries only allowed for visits up to 48 hours, news agency Reuters reports.