The Duke of Cambridge has spoken about the importance of young people learning about mental health during the first stop on the royal tour of Pakistan.

Prince William and the Duchess of Cambridge met boys and girls at a government-run college in Islamabad on the first full day of their visit.

The prince said pupils from disadvantaged backgrounds did not have a "stable health platform".

The couple also met Pakistan's Prime Minister Imran Khan for lunch.

Kensington Palace said political tensions and security concerns meant the tour was the couple's "most complex" to date.

The five-day trip was organised at the request of the Foreign and Commonwealth Office.

The couple are the first royals to officially visit the Commonwealth country since the Prince of Wales and Duchess of Cornwall visited the region in 2006.

As they left the Islamabad Model College for Girls, Prince William said to a teacher: "In the UK we're trying to make sure mental health is part of education as well."

He said students from disadvantaged backgrounds did not have a "stable health platform to build on" and that education in this area was important.

The royal couple, alongside the Duke and Duchess of Sussex, regularly campaign about raising mental health awareness. Last week the Every Mind Matters website crashed following the foursome's appearance in a film to promote the mental health support initiative.

'Big fans of Diana'

The prince's tour of Pakistan follows in the footsteps of his parents. His father, the Prince of Wales, visited in 2006 and his mother Diana, Princess of Wales, went on several charity work trips there before her death in 1997.

One pupil at the visit to the college told Prince William she and her classmates were "big fans of your mother".

"Oh, that's very sweet of you. I was a big fan of my mother too," the duke said.

"She came here three times. I was very small. This is my first time and it is very nice to be here and meet you all," he added.

Prince William and Catherine's visit to the school in Islamabad involved them learning about girls' education in Pakistan.

A local education officer, Mohammed Sohailkhan, told reporters the quality of education varied across Pakistan.

"I can't paint you an entirely rosy picture," he said. "It does still fluctuate wildly, particularly in rural regions, where there has traditionally been cultural barriers towards this, notably in terms of sending girls away to college.

"But these barriers are slowly being broken down."

What are William and Catherine doing here in Pakistan? Put simply they are spreading a little royal love around the place.

It's been 13 years since a royal visit. Some of those have been very tough years for Pakistan, a country that Britain has strong and long historical links with. Around one-and-half million British citizens are of Pakistani descent. Part of the visit is about giving the country a royal hug and showing people here that Britain cares.

It's also a way of highlighting joint interests - climate change threatens Pakistan more than most, early years education is one of the duchess's biggest single concerns, and security is a key part of the co-operation between the UK and Pakistan.

And it is a way of selling Pakistan to the world. The duke and duchess will leave the cities and see something of the spare and rugged countryside.

Yes, there's lots of security surrounding the couple. But their travels will also advertise the breathtaking beauty of Pakistan, alongside the bustling cities. It is an opportunity to learn, to encourage and to give something back.

The British High Commission said UK aid in Pakistan had helped more than five and a half million girls receive a quality education since 2011.

The duke and duchess heard how pupils were benefiting from the Teach for Pakistan programme - a fast-track teacher training scheme modelled on the UK's Teach First scheme.

The prince and his wife also visited the Margalla Hills National Park in the foothills of the Himalayas, before travelling to Mr Khan's official residence in Islamabad for a private lunch.

Mr Khan, a former international cricketing star turned politician, was a friend of the prince's mother.

Prince William and Mr Khan reminisced about meeting each other when the duke was a boy at a gathering in Richmond, south-west London, in 1996.

Prince William and Catherine will attend a reception on Tuesday evening with guests from Pakistan's business, music and film industries, as well as members of the government.

In a speech at the reception, William is expected to say that the UK and Pakistan share "unique bonds".

"You can always rely on the UK to keep playing an important role as a key partner and friend," he will add.