"We are deeply concerned about the imprisonment of human rights activist Hu Jia and have pressed the Chinese authorities for his immediate release on many occasions and at the highest level," said State Department spokesman Gordon Duguid.
"We hope that the recognition the European Parliament has given Hu Jia by awarding him the prestigious Sakharov Prize will demonstrate to China's leaders the enormous esteem the international community holds for his important work as a human rights defender and that China will release him immediately."
The European Parliament named Hu, 35, its Sakharov laureate for this year despite pressure from China, which denounced it as "gross interference" in its domestic affairs a day before a two-day Asia-Europe Meeting (ASEM) summit in Beijing.
Duguid said: "We will continue to work with others in the international community to encourage China to bring its human rights practices in compliance with international human rights standards."
"No one should be imprisoned for expressing his or her views or for working within China's legal system to improve the life of his or her fellow citizens," the spokesman added.
"We look forward to the day when China will recognize the contribution of Chinese human rights activists who work on some of the most difficult problems facing Chinese society."
Separately, the State Department urged China to swiftly release Beijing house church leader Zhang "Bike" Mingxuan after he was reportedly detained in southwest China and his two sons were beaten in Beijing.
"We call upon the government of China immediately to release pastor Zhang and permit his family members to return home, to condemn the violent acts committed against his sons, and to bring to justice those individuals responsible for such acts," it said.
In a letter to Secretary of State Condoleezza Rice, congressmen Frank Wolf and Christopher Smith said Zhang was detained in Kunming city, southwest China, on October 16, followed three days later in Beijing by his wife.
They also alleged that his son Zhang Jian was "severely beaten" unconscious when police raided the family's home in Beijing, with injuries so serious that he may lose sight in his right eye. A younger son was also beaten, they added.
"Should the administration fail to act on this case, it will serve as a symbol of the broken promises President Bush made to promote freedom and democracy throughout the world," the congressmen said in their letter dated Wednesday.
The State Department said: "We are concerned about a pattern of intimidation of religious freedom and rule of law advocates and their family members.
"We urge China to honor those international human rights instruments to which it is a signatory that protect the rule of law, freedom of expression, and freedom of religion."
Nicknamed Pastor Bike for having travelled China by bicycle to distribute Bibles and preach the Christian gospel, Zhang -- one of best known leaders of China's unofficial house churches -- and his wife were previously detained before the Beijing Olympics.