No one values the freedom and opportunities of America more than me: Melania Trump

Melania Trump, the wife of US Republican presidential candidate Donald Trump, said on Thursday she would work to improve a social media culture that "has gotten too mean and too rough, especially to children and teenagers" if she becomes First Lady.

Trump, who was born in Slovenia and became an American citizen in 2006, said that becoming a United States citizen was "the greatest privilege in the world".

"I'm an immigrant, and no one values the freedoms and opportunities of America more than me," CNN quoted her as saying.

In a rare appearance on the campaign trail she discussed her vision for her role in the White House for the first time in suburban Philadelphia.

"It is never OK when a 12-year-old girl or boy is mocked, bullied or attacked. It is terrible when it happens on the playground, and it is absolutely unacceptable when it is done by someone with no name hiding on the internet. We have to find a better way to talk to each other," Melania Trump said.

"We must find better ways to honour and support the basic goodness of our children, especially in social media," she said. "It will be one of the main focuses of my work, if I am privileged enough to become your First Lady."

However, she made no allusion to her husband's long history of bullying political foes, journalists and entertainers on Twitter.

In September, after Democratic presidential candidate Hillary Clinton cited Trump's reference to 1996 Miss Universe Alicia Machado as "Miss Piggy" and "Miss Housekeeper" during their first presidential debate, Trump said in a 3 am. Twitter rant that Machado is "disgusting" and a "con" and directed followers to check out a non-existent Machado sex tape.

It was Melania Trump's first speech since her appearance at the Republican National Convention, where her remarks triggered controversy because one section plagiarised Michelle Obama's 2008 Democratic National Committee speech. A speechwriter later apologised.

She cast her husband as someone who's in touch with America's working class.

"Every time my husband learnt of a factory closing in Ohio or North Carolina or Pennsylvania, I could see him get very upset," CNN quoted her as saying as she made the case that the Republican candidate can fix the nation's economic woes.

Her speech on Thursday was the first of what Donald Trump said in an interview with ABC would be two or three major speeches before the November 8 election.

The speech took place in Berwyn, Pennsylvania — in the suburbs of Philadelphia — and was designed to help Trump win over the middle-class women in the region who could tip the balance of Pennsylvania's 20 electoral votes for Trump or Clinton.