Tibetan writer and human rights advocate Tsering Woeser, and her husband Wang Lixiong, a Chinese scholar of ethnic issues, have been placed under house arrest at the couple’s Beijing home, Reuters reported Wednesday.

Woeser claimed that she was detained after she got a call from the U.S. embassy on Sunday, inviting her to meet a U.S. official for dinner on Tuesday. The decision to place the activist couple under house arrest comes at a time when U.S. Secretary of State John Kerry is in Beijing for the sixth U.S. - China Strategic and Economic Dialogue. Chinese security officers arrived at the couple’s residence on Tuesday, soon after they returned from a trip to Mongolia, Woeser posted on Facebook Tuesday night.

“They said that they would be taking up their posts for the next two days and that we were forbidden to go out. I asked for a reason and they said that it was confidential,” she wrote. She also told Reuters that there were two police officers guarding their elevator and a few more had been stationed on the ground floor of her building.

Woeser, a Tibetan by birth, maintains a website called Invisible Tibet in which she posts articles and poems advocating freedom for Tibet. Her husband, Wang, has written several books on Tibet that have been critical of China.

“Knowing that I was on the road and couldn’t participate, they’d set the date for the next day. I didn’t know whom I’d meet, but regardless of whom I would have met, I was already prevented from doing so by the state security,” Woeser wrote on Facebook.

This is not the first time that the Tibetan activist has been detained by Chinese law-enforcement agencies. In 2013, when Woeser was given the International Woman of Courage Award by the U.S. State Department, she was confined to her home and was not provided a passport to travel to the U.S.

Woeser wrote in her Facebook post that Kerry had written her a letter afterwards. “If I were to see him on this occasion, I would very much like to reply to his letter and express my thanks. But most regrettably, I am at home under house arrest.”

Woeser and Wang had earlier been placed under house arrest during the Tibetan unrest of 2008, for talking to reporters.