Police in northern China have arrested two citizen activists who took to the streets with placards reading: “The government has a duty to control smog”.

Feng Honglian and Zhang Hui were taken into custody on Sunday, one day after China’s environment minister promised to “guarantee the public’s rights to supervise the fight against air pollution”.

Earlier in the day, the pair had been among a small group of activists who held an anti-pollution protest in Xi’an, the capital of Shaanxi province.

Photographs posted on the internet show the campaigners wearing face-masks and holding posters with slogans including: “Smog causes cancer and harms everyone”.

Communist Party leaders have made bold statements about their commitment to protecting the environment this week at the annual meeting of China’s tightly controlled parliament in Beijing.

“We are going to punish, with an iron hand, any violators who destroy ecology or environment, with no exceptions,” Xi Jinping, the president, said on Friday.

The following afternoon Chen Jining, a respected academic who recently became environment minister, vowed to give citizens a greater role in the fight against smog.

Mr Chen said his guiding principle would be: “Prevention, prevention, prevention”.

However, those messages were undermined when Chinese propaganda chiefs ordered websites to delete Under the Dome, a viral documentary about pollution.

The film was released on February 28 and initially appeared to enjoy official support but was scrubbed from the internet on Friday afternoon after it had been viewed hundreds of millions of times.

Many believe Beijing’s decision to erase the film stemmed from concerns about the level of criticism of the government it was generating.

Under the Dome appeared to have been the inspiration for Sunday’s protest outside government headquarters in Xi’an, said Luo Guangming, a resident who knows both Mr Zhang and Ms Feng.

“I guess that after the release of Under the Dome, people became more enthusiastic about environmental issues,” he said.

“From what I’ve seen, there have been heated online discussions in which some people think we are all responsible for the smog while others think the government should be held responsible. I imagine that after the debate the idea of a campaign came naturally.” Mr Zhang, who is in his 50s, was taken to the city’s Changlefang police station at around 4pm on Sunday, according to *Weiquanwang**, **a* human rights website. Ms Feng, who teaches at a local university, was detained at around 11pm on Sunday night after posting an online message in which she took responsibility for organising the protest. Both share an interest in environmental issues, Mr Luo said.

China is in the midst of a wide-ranging crackdown on dissent that has seen lawyers, academics, social activists, religious leaders and most recently feminist campaigners detained or jailed.

Calls to the police station where Mr Zhang is thought to be went unanswered. An official at another station where Ms Feng is thought to be said he had no information about her.