Donald Trump has accused former President Barack Obama of aiding the formation of a violent street gang with his "weak illegal immigration policies".

Taking to Twitter he said his predecessor's administration had "allowed bad MS 13 gangs to form in cities across US", but promised that his regime was "removing them fast!”

He did not provide any evidence to back up his claim.

MS-13 is a street gang based largely in Los Angeles, although it has operations in a large number of US states. Its members have been convicted of a litany of crimes, including drug distribution, murder, rape, prostitution, and robbery

Its membership is composed primarily of immigrants from Central American countries like El Salvador, Honduras, Mexico and Guatemala, according to the FBI. However, people from other Central and South American are known to have joined.

The Bureau also said the gang formed in the late 1980s. Mr Obama took office in January 2008, when the FBI described the gang's growth as "moderate".

The FBI estimated MS-13 membership stands at about 6,000 to 10,000 in 2008. That number had not changed by 2017, according to a Fox News report citing the US Attorney’s Office.

Mr Obama deported more than 2.5 million people during his term in office - more than any other president in history (although that record is complicated by a change in the official definition of “deportation”).

The former president's administration was also responsible for changing immigration enforcement policies to prioritise convicted criminals, according to the Migration Policy Institute.

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The number of immigrants arrested doubled in the weeks after Mr Trump took office, with 21,362 picked up between 20 January to 13 March. This was largely due to an increase in the arrest of non-criminals, which doubled under the same time period.

The Trump administration has increased efforts to combat illegal immigration in recent months, expanding the scope of immigrants who can be targeted for deportation and pledging more funding for border control programmes.