Chongqing Vice Mayor Wang Lijun is being investigated after visiting the U.S. consulate in Chengdu. (AP/AP)

China’s Foreign Ministry confirmed Thursday that Wang Lijun, vice mayor of the sprawling southwestern city of Chongqing, spent one day at the U.S. Consulate in nearby Chengdu and that he is now under official investigation in a bizarre episode with potential bearing on China’s upcoming leadership transition.

The official Xinhua News Agency reported late Thursday, citing the Foreign Ministry’s spokesman’s office, that “Wang entered the U.S. general consulate in Chengdu on Feb. 6 and left after staying there for one day.”

The report, on Xinhua’s Chinese- and English-language Web sites, was the Chinese government’s first acknowledgment that Wang — a former police chief renowned for tackling organized crime in Chongqing — had been at the consulate.

On Wednesday, State Department spokeswoman Victoria Nuland told reporters in Washington that Wang had gone to the Chengdu consulate to meet with U.S. officials and had left “of his own volition.”

Reports throughout the day Thursday in China’s official news media said Wang was suffering from “depression” and had been placed on medical leave. But the Internet was rife with unconfirmed speculation that Wang had gone to the U.S. mission to request political asylum, perhaps fearing he was about to be targeted for corruption.

The case of the vice mayor has taken on broader significance because of his close ties to Chongqing’s Communist Party chief, Bo Xilai, a colorful figure in the party hierarchy who has been widely tipped for elevation to a spot on the powerful nine-member Politburo Standing Committee.

Bo made his mark in Chong­qing in a controversial “hard strike” campaign against organized crime, with Wang as his top police enforcer. While the crackdown was popular with the public, human rights lawyers and others were critical, saying that the police ignored individual rights and targeted some innocent people.

Bo also made headlines here — and some enemies — with his flamboyant style, including a “Red Culture” campaign in which he encouraged Chongqing residents to gather in public parks on weekends and sing old Communist Party songs. He also ordered the local Chongqing TV station to drop sitcoms and begin broadcasting “patriotic” programs.

Some analysts saw Bo’s efforts as a means of self-promotion in advance of this year’s leadership transition. The mystery surrounding Wang — whether he actually tried to seek political asylum and if so, why — gave rise to speculation about a power struggle in the Communist Party’s top ranks.

China’s Communist Party often uses corruption allegations to remove unwanted officials from prominent positions.

According to the power struggle theory, if someone were determined to stop Bo’s rise, he or she may have gone after Wang to discredit Bo.

“It’s an earthquake event in Chinese elite politics, with the potential to change the balance of power among competing factions,” said Cheng Li, an expert on China’s political leadership with the Brookings Institution in Washington.

The party-owned Global Times newspaper reported Wednesday that the intrigue in Chongqing had begun a week earlier, when the Chongqing government announced that Wang was being removed from his public security role but keeping his title of vice mayor and taking charge of education and environmental protection.

The paper said Wang visited the campus of Chongqing Normal University on Sunday, the day before he is now said to have gone to the U.S. Consulate in Chengdu.