The United States ambassador to China called on Beijing Monday to release from jail the crippled rights defender Ni Yulan and her husband, and to end the house arrest of their daughter.

A Beijing court convicted Ni and her husband Dong Jiqin last week of "provoking trouble" after the couple had worked to protect alleged victims of government-backed land grabs, a leading cause of social unrest in China.

The couple were detained in April last year as authorities sought to crackdown on dissent amid calls on the Internet for Arab Spring-style protests in China.

Ni, 51, who has been wheelchair-bound since an alleged police beating in 2002, was sentenced to two years and eight months prison, while Dong received two years. It was the third time Ni has been jailed since 2002.

"I am very concerned by the sentencing of property and petitioner rights advocate Ni Yulan and her husband Dong Jiqin, as well as Ms Ni's health and well-being, particularly in light of past abuses she has suffered," Gary Locke said in a statement.

"I call on China's authorities to release Ni Yulan and Dong Jiqin, and to cease any restrictions on the freedoms of their family members."

Locke expressed concern over the "extra-judicial house arrest" of the couple's daughter, Dong Xuan, who was placed in police custody last week. AFP was unable to reach the daughter on Monday.

Their lawyer Cheng Hai welcomed the statement from Locke and expressed hopes that it would help the couple in their appeal.

Ni's case has been championed by numerous Western governments, including the United States and the European Union, which sent representatives to meet with her during a brief period of freedom ahead of her latest arrest.

The EU called for Ni's release immediately after her conviction.

China's foreign ministry spokesman Liu Weimin on Monday refused to directly comment on the demands of the EU and US, and would only say: "We hope relevant countries will respect China's judicial sovereignty."

Cheng said Ni's meeting in early 2011 with then US ambassador Jon Huntsman was cited by police and prosecutors as a "political" element leading to her conviction.

"During the trial, I stated that China and the United States enjoy normalised relations, we are like friends," Cheng told AFP.

"I said that it is normal for ambassadors to China to meet ordinary people... and that it would be a mistake to label such meetings as 'political'."

Ni and Dong lodged their appeal on Friday last week, Cheng said.