WASHINGTON: An advocacy group is offering Donald Trump "sensitivity training" after the Republican presidential candidate "appeared to mock" a New York Times reporter with a disability.

At issue is what The New York Times interprets as Trump's attempt on Tuesday to “ridicule the appearance” of journalist Serge Kovaleski.

Trump challenged recollections by Kovaleski and others about the 9/11 aftermath during a speech, having made unsubstantiated claims that thousands of Muslims in New Jersey were seen "celebrating the attack".

Trump, whose voice took a mocking tone, said, “Poor guy, you ought'a see this guy,” then gestured in a jerky fashion as if imitating Kovaleski's movements.

The Times expressed outrage afterward that Trump would “ridicule the appearance of one of our reporters.”

Jay Ruderman of the Ruderman Family Foundation in Boston said Thursday that Trump should apologize to Serge Kovaleski of The New York Times and the public, adding that Kovaleski has a congenital condition affecting joint movement.

Ruderman said Trump would benefit from a “series of sensitivity training sessions” and offered to provide them to help him better understand people with disabilities.

“It is unacceptable for a child to mock another child's disability on the playground, never mind a presidential candidate mocking someone's disability as part of a national political discourse,” he said.

This is not the first time that the the Republican front-runner has mocked people, including the Muslim community as a whole.

In August, while speaking to a crowd outside Norwood, Massachusetts, Trump hit Mrs Clinton and lodged multiple attacks on Huma Abedin, saying the aide should not have had access to the kind of information she did while Clinton was secretary of state.

Read more: Trump attacks Clinton’s Muslim aide, her husband

He also chastised Anthony Weiner, Abedin's husband, calling him a “perv”, a newspaper report said.

The presidential candidate said in October that if he was elected president he would send back Syrian refugees taken in by the US because they "may be the self-styled Islamic State (IS) militants in disguise".

Read more: Trump says he'd send back Syrians taken in by US

It was reported last week that Trump wants to shut down mosques in the United States.

He says he has a plan to counter ‘jihadist’ ideology in America: Tear apart the First Amendment of the American constitution on which this country is founded.

He voiced his support for creating a mandatory database to track Muslims in the United States, after an escalating series of responses following the deadly attacks in Paris.

He said Muslims would be signed up at "different places," adding, "It's all about management."

Also read: 5 ways American Muslims should counter Trump’s narrative

The billionaire businessman, the front-runner in the race to become the Republican party's White House nominee, has raised hackles with his controversial comments on immigration, gun control and women, among other issues.

In an interview on CBS television's "60 Minutes" news programme, US President Barack Obama expressed certainty that Trump would not be the next president of the United States.

"He knows how to get attention. He is, you know, the classic reality TV character, and at this early stage, it's not surprising that he's gotten a lot of attention,"