The capital city's environmental watchdog has urged the country's two leading universities to retire their coal boilers and use green energy.

"All of the capital universities in six urban districts are now ready to phase out coal boilers except Peking University and Tsinghua University," Du Shaozhong, deputy director of Beijing municipal environmental protection bureau, told China Daily through a telephone interview on Sunday.

Though the two universities had earlier told the local media they would speed up the switch to green energy, Du said he could not rest assured until the concerned varsities took "practical actions" in that direction.

"They did not give me an official response about the modification deadline," he said on Sunday afternoon. "The negotiation with Tsinghua has reached a stasis in the last two years."

He urged students to participate in the green energy promotion campaign as he spoke on the air quality in Beijing at Tsinghua on Thursday.

His speech has spurred on discussions in the media.

As a response, Zhang Yimin, director of the heating supply center of Peking University, told the local media that the university will switch to green energy in the spring of 2012.

"We have ordered four new boilers fueled by gas to take the place of the four coal boilers now in use after this winter season is over," he told Beijing Evening News on Friday.

He said it was tough to upgrade boilers during the heating season, and that using green energy might prove to be twice as expensive.

At present the cost of keeping Peking University warm in winter is about 20 million yuan ($3 million) a year, and it has not received a government subsidy to switch to green energy, according to the report.

The report also said Tsinghua University said they would finish upgrade of boilers before 2014.

However, the logistics management department of Tsinghua refused to confirm the plan with China Daily on Sunday faced with a flurry of questions about whether it had a prerogative to postpone their boilers' modification.

"I have noticed yellow smoke rising out of a chimney in campus since 2008, though most of the time it produces white smoke," Zhu Shaojun, a student of Tsinghua school of journalism and communication, told China Daily on Sunday.

"Our university is located not far from the Beijing Olympic stadiums. So I wonder how it could be a polluter like what the city's environmental watchdog have said it was," he said.

Chu Xiaowei, a 25-year-old student of the school of electronics engineering and computer science under Peking University, said, "It is shameful and unbelievable to hear from media reports that our university is falling behind when it comes to preventing pollution."

"I am so surprised because the university always teaches us to be citizens aware of the importance of protecting the environment," he said.

Beijing has seen three less "blue sky days" in the past 11 months of the year, compared to the same period last year, according to the Beijing municipal environmental protection bureau.

The city still needs to have 13 more "blue sky days" to reach its target of 274 this year.

In a move to reduce emission of pollutants, the bureau has been keeping a close watch on construction sites and coal-fired boilers since Beijing switched on the central heating system in mid-November.