The daughters of five imprisoned Chinese activists appealed Thursday before the US Congress for their fathers' freedom, saying they have also suffered through Beijing's decisions.

Testifying before a House of Representatives committee, the exiled daughters spoke of surveillance while they were still in China and, later, the pain of learning of their fathers' treatment in prison.

Grace Geng, whose father Gao Zhisheng is one of China's best-known human rights lawyers, said that Chinese police accompanied her to school -- even following her to the restroom. Geng, now 20, fled with her mother and brother to the United States in 2009.

Gao -- who defended some of China's most vulnerable people including aggrieved villagers, underground Christians and members of the banned Falungong spiritual movement -- has previously spoken of physical abuse in detention. He has not been heard from since January when an uncle visited him in prison.

"I want to let you know that my father is still behind the bars and my mom is in poor health, struggling to support the family," Geng said.

Asked by a lawmaker if she had a message to China's president, Geng said: "Yes, I want to say to Xi Jinping... please release our fathers so they can come back with us."

Ti-Anna Wang, whose dissident father Wang Bingzhang is a US permanent resident but is serving a life term in China, called on US leaders to raise the prisoners' cases more forcefully.

"I believe high-level diplomacy is our fathers' best chance for freedom," she said.

Also appealing for their fathers' freedom were the daughters of Peng Ming, a reform-minded former official whose family says he was kidnapped to China from Thailand; Liu Xianbin, who is serving a 10-year jail term after posting pro-democracy articles, and Wang Zhiwen, a former railway engineer who practices Falungong.

Representative Chris Smith, who chaired the hearing, said that China's treatment of political prisoners caused "loss, bewilderment, emotional pain and agony" to their families.

"In a very real sense, everyone close to a prisoner of conscience goes to jail and lives a seemingly unending nightmare," Smith said.