Islamic extremists in Somalia have branded Donald Trump a ’brainless billionaire’.

In a new video, militant group al-Shabaab verbally attacked the US president as his administration steps up military efforts against them.

The new video said US voters elected ‘arguably the most stupid president a country could ever have’ and said Mr Trump is ‘making the United States the greatest joke on Earth and is now propelling it further to its eventual defeat and destruction’.

The SITE Intelligence Group said the video also addresses next month’s presidential election in neighbouring Kenya.

The al-Qaida-linked al-Shabaab has claimed a growing number of deadly attacks in Kenya as the election approaches, with Kenyan president Uhuru Kenyatta declaring a new offensive against the extremists this month.

Earlier this year, Mr Trump approved expanded military operations against al-Shabaab, including more aggressive air strikes and considering parts of southern Somalia areas of active hostilities.

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Somalia is also included in Mr Trump’s ban on refugees and visitors from six mostly Muslim countries.

The extremist group has vowed retribution on Kenya in particular for sending its troops to Somalia to take part in a multinational African Union force against al-Shabaab.

View photos Donald Trump is the subject of a new video from extremists in Somalia (Picture: Rex) More

‘Your military’s invasion of Somalia will continue to destabilise your country,’ the new al-Shabaab video said.

‘When we do strike, your government will not be able to protect you.’

The extremist group killed more than 4,200 people last year, according to the Africa Centre for Strategic Studies.

Al-Shabaab has vowed to step up attacks against Somalia’s recently elected government and has carried out numerous deadly attacks in the capital, Mogadishu.

Pressure is growing on Somalia’s military to assume full responsibility for the country’s security.

The 22,000-strong African Union multinational force, which has been supporting the fragile central government, plans to start withdrawing in 2018 and leave by the end of 2020.

However, the US military has expressed concern that Somalia’s forces are not yet ready.