Angelina Jolie has made her Instagram debut using her first post to highlight the plight of young women in Afghanistan since the Taliban takeover.

The actress gained more than 1.8 million followers within two hours of joining the social media platform after posting pictures of a letter she had received from a teenage girl in Afghanistan.

The 46-year-old, who is a special envoy for the United Nations High Commissioner for Refugees, anonymised the letter, which details the young woman's fears about living in the country.

The teen wrote about the difficulties of going to school because of Taliban controls, stating: "We all lost our freedom and we are imprisoned again."

She also says: "We all had rights, we was able to defend our rights freely but when they (the Taliban) came, we are all afraid of them and we think all our dreams are gone."

Jolie said she feared Afghan people "are losing their ability to communicate on social media and to express themselves freely" following the takeover of the country.

"So I've come on Instagram to share their stories and the voices of those across the globe who are fighting for their basic human rights," she added.

Her short biography on the site noted that as well as working with the UN she is also a mother and filmmaker.

"I was on the border of Afghanistan two weeks before 9/11, where I met Afghan refugees who had fled the Taliban. This was 20 years ago," she wrote.

"It is sickening to watch Afghans being displaced yet again out of the fear and uncertainty that has gripped their country.

"To spend so much time and money, to have bloodshed and lives lost only to come to this, is a failure almost impossible to understand.

"Watching for decades how Afghan refugees - some of the most capable people in the world - are treated like a burden is also sickening."

She added: "Knowing that if they had the tools and respect, how much they would do for themselves. And meeting so many women and girls who not only wanted an education, but fought for it.

"Like others who are committed, I will not turn away. I will continue to look for ways to help. And I hope you'll join me."

The post also includes a photo of seven Afghan women, facing away from the camera.

Last week, the Taliban took control of Afghanistan's capital of Kabul, signalling a collapse of the country's government.

Since then thousands of people have been trying to flee the country, with desperate mothers seen handing their children to troops and people hanging on to planes.