Image copyright Getty Images Image caption BTS sing about issues including bullying and mental health

South Korean boy band BTS have become the first K-pop group to win a prestigious US Billboard music award.

The seven-member group - known as Bangtan Sonyeondan in Korean or "Bulletproof Boy Scouts" - won Top Social Artist, voted for by fans.

They beat Justin Bieber, Selena Gomez, Ariana Grande and Shawn Mendes in the category.

The win marks a breakthrough for the K-pop genre, which has long tried to crack Western markets.

"We still cannot believe that we are standing here on this stage at the Billboard Music Awards," the group said in their acceptance speech.

"It's so great to see all the artists we admire. To be in this category with such great artists, [we are] just really honoured."

The band - made up of members Jin, Suga, J-Hope, Rap Monster, Jimin, V and Jungkook - later tweeted that the win was a "dream come true".

The group use hip hop and R&B styles to sing about issues including bullying and mental health. They have released albums in Korean and Japanese and have almost 10 million followers on social media.

Image copyright @BTS_twt Image caption "Our dream has come true," the band tweeted following their win

Despite not singing in English, BTS have already toured the US and sold out venues in Los Angeles, Chicago and New York.

Their success marks a high point for Korean music in the West following South Korean rapper Psy's 2012 global hit Gangnam Style, which has so far racked up almost 3 billion views on YouTube.

Psy then concentrated on the huge Chinese music market, collaborating with pianist Lang Lang for a series of smash hits there, although in 2014 he did release Hangover alongside US rapper Snoop Dogg, which has had almost 300 million YouTube views.

K-pop was conceived in South Korea in the 1990s as a Western-Asian hybrid and is now a multi-million dollar industry, part of the so-called 'Korean Wave' - the spread of Korean music, drama and film to the rest of the world.

Large numbers of boy and girl bands attempt to make their mark each year.

However, there has been controversy over the extent of control exerted over the young stars by their record companies. Members of some groups are expected to abide by a set of behavioural rules.

Discussing politics has also been considered taboo - Chou Tzuyu, a 16-year-old Taiwanese singer and dancer in the Korean girl group Twice, was required by her record company to issue a video apology for waving a Taiwanese flag ahead of the island's election last year.

JYP Entertainment denied coercing her into the apology to appease audiences in mainland China, which sees Taiwan as a renegade province.

Observers say the incident may have helped Tsai Ing-wen, from the traditionally pro-independence Democratic Progressive Party, win a landslide to become Taiwan's first female president in 2016.