BEIJING — Police have detained an activist singer who wrote that she wanted to blow up a government agency seen as inept, a friend said Wednesday. The singer's supporters said she would never have carried out the threat and is being targeted for her critical views.

Wu Hongfei was detained Monday by Beijing police on the charge of "causing trouble," likely because of a post on her microblog, said Hu Jia, an activist who is friends with Wu.

Last weekend, Wu wrote on her microblog that she would like to blow up government housing commission offices. In the post since removed by censors, Wu berated those who work for the agency.

She did not explain the reason for her post, but in an era when many young Chinese adults are complaining about difficulty buying homes, such agencies are widely perceived as being ineffective in ensuring the supply of affordable homes.

The post was made shortly after a man set off a bomb at Beijing's airport, a blast that injured no one but the accused bomber.

Beijing police did not respond to a request to verify Wu's detention.

Chinese authorities have been known to arrest, convict and jail those who make bomb threats on charges of spreading terrorist rumors.

New York-based Human Rights Watch said it is likely Wu's detention was political retribution for her past criticisms of the government.

"The Chinese government has frequently used criminal charges to punish and intimidate individuals for expressing opinions critical of the government. Wu has been very outspoken in the past, and it is hard not to suspect that her criminal detention is the result of political retribution," said Maya Wang, a researcher for the group.

Hu said Wu has been targeted because the authorities want to deter further discussions of Ji Zhongxing, the 33-year-old man accused of setting off the homemade bomb at Beijing Capital International Airport on Saturday. Ji's brother says the man suffered a beating in 2005 that left him paralyzed from the waist down and had grown frustrated after years of unsuccessfully trying to seek redress.

Since the blast, police have also detained two men who threatened to blow up the airport and a video arcade respectively.

Hu said authorities have singled out the singer, Wu, partly because she has been outspoken against social ills in the past. She has a relatively strong following on social media with nearly 120,000 followers on her microblog hosted by Sina Weibo, a Twitter-like service.

Also on her microblog, Wu had written that she hoped Ji can live on with dignity.

"If he is a thug, I wish this government would foot the bill for this thug. It is not that I encourage violence, but I extremely detest the system that pushes innocent people to violence. Justice is everyone's reasonable appeal," Wu wrote.