Angry parents have pledged to withdraw their sons from Boy Scouts amid an outcry over Donald Trump's highly politicised speech to tens of thousands of youngsters.

The US President broke with tradition to attack his political foes, threaten to fire federal employees, and denounce the media in a rambling address at the 2017 National Scout Jamboree.

His speech, which also contained innuendo-laden anecdotes, was likened by one commentator to that of "a drunk stepdad".

Previous presidents to have addressed the Jamboree, held every four years, have typically steered clear of politics and instead saluted Scout values such as trustworthiness, loyalty, and bravery.

Many parents called on the Boy Scouts of America to condemn Mr Trump's speech and were further angered by the organisation's lukewarm response.

"The Boy Scouts of America is a wholly non-partisan and does not promote any one position, product, service, political candidate or philosophy," the group said in a statement, adding it was "long-standing custom to invite the US President to the National Jamboree".

Thousands of people have posted angry comments on the organisation's social media pages since Monday night's speech in West Virginia.

"I will be pulling my son out of Scouting after the silence following the political indoctrination at the Jamboree. Shame on you for allowing this to go unchallenged," wrote Marc Frischhertz wrote on Facebook.

Donald Trump's speech at the National Scout Jamboree was watched by a crowd of 40,000 people (Reuters)

Jude Nevans Cleaver said: "I want you to know that as of this moment, my son is being pulled out of Boy Scouts. You apparently got very confused about what makes for a good role model."

John Footen added: "I am now suddenly questioning whether Scouts represent [the] values that I want my children to learn if this is someone they put forward as a role model with no qualification or cautions to the children."

One Twitter user said her family was withdrawing 14 boys from the Scouts "after what was basically [a] Hitler Youth rally".

The President's speech was watched by a crowd of 40,000 people including tens of thousands of boys aged between 12 and 18.

While he praised Scouts as having "character and integrity" and lauded the virtues of "hard work and perseverance," Mr Trump's 35-minute speech also repeatedly touched on politically loaded themes.

He decried the healthcare law championed by his predecessor, Barack Obama, regaled the crowd of cheering boys with his take on the "incredible night with the maps" when he was elected in November, and encouraged them to boo Hillary Clinton.