Three graffiti artists hired by producers of hit US television drama Homeland to give its sets more realism have instead caused embarrassment by using their artwork to accuse the show of racism.

Artists Heba Amin, Caram Kapp and Stone were asked to mark up the walls of a set depicting a Syrian refugee camp for episodes of the show's fifth season, which were filmed in Berlin.

They decided to use the chance to voice their displeasure with its depiction of people from the Middle East and Asia.

"Homeland's representation of people from the Arab and Muslim world... has on several occasions erred," Kapp told AFP from Berlin.

"It has painted Muslims mainly as antagonists and the protagonists are allowed to torture and murder them."

In the second episode of the latest series, main character Carrie Mathison, played by American actress Claire Danes, can be seen walking past a breeze-block wall on which is written in black spray paint: "Homeland is racist".

Other slogans called the show "a watermelon" -- Arabic vernacular indicating something farcical -- and included the social media hashtag #BlackLivesMatter, which has become the rallying cry of the US movement outraged over police killings of unarmed African Americans.

Kapp said the three artists were encouraged by producers to "come up with our own material" and were given free rein over what they wrote, providing it wasn't political.

"Our intention with this was to generate a discussion," he said. "It was also a call for a more differentiated representation of people from the Middle East and South East Asia."

The show is no stranger to controversy, having drawn derision during its second season for featuring a joint plot between Al-Qaeda and Lebanese Shiite movement Hezbollah -- two groups currently waging fierce battles against each other in Syria.

Kapp said he and his fellow artists were concerned they would be rumbled by producers on set, but said it was "an opportunity we wouldn't have been comfortable" to miss.

"We never thought the episode would air," he said. "We thought someone would look in the edit and we were very surprised to find that this made it in."

In a statement posted on Amin's website, the trio, while admitting Homeland "looks good and is well-acted and produced" said it had "garnered the reputation of being the most bigoted show on television".

Showtime, the series' makers, has yet to comment on the graffiti.