Chinese dissident Chen Guangcheng on Tuesday accused Beijing authorities of cracking down on members of his family, calling on President Barack Obama to intervene.

Chen, who emigrated to the United States last year following his dramatic escape from house arrest, told reporters at the National Press Club in Washington that several members of his family had been harassed since he left his homeland.

The 41-year-old rights activist cited the prominent case of his nephew Chen Kegui, 33, who had been detained and "tortured" before being sentenced to three years and three months in prison without any access to a lawyer.

Chen Kegui was sentenced for "intentionally inflicting injuries" to local Communist Party officials who had stormed into his home during a raid.

The rights group Freedom Now lodged a petition with the United Nations on Tuesday urging the release of Chen Kegui, saying his life and health was "in serious danger."

Chen Guangcheng, meanwhile, said other members of his family, including a four-year-old nephew, were subjected to surveillance and harassment on a regular basis.

He said his elder brother was physically attacked and had the tires of his car slashed. Local authorities paid a gang of thugs to wreck the garden of the family home, hurling stones, bottles and dead animals into the property, he added.

A self-taught lawyer who has been blind since childhood, Chen angered authorities in the eastern Chinese province of Shandong by exposing abuses under China's one-child population policy.

He was sentenced to four years in prison and was later placed under house arrest. He said he and his wife were beaten for continuing to speak out.

He escaped from house arrest in April last year and took refuge at the US Embassy in Beijing before later emigrating to New York with his wife and children.

Chen Guangcheng said Tuesday China had failed to deliver on a promise made to US authorities to investigate "abuse and injustice" suffered by him and his family.

The rights situation had in fact worsened, with more than 140 activists arrested since Obama met Chinese President Xi Jinping on the sidelines of the G20 summit in Stockholm earlier this month, Chen said.

"While I so am grateful for Mr. John Kerry the Secretary of State, and his effort to help me and my family members in this regard, we have not seen any obvious progress" on human rights violations, Chen said

"So I call on the president, Mr. Obama, to extend the foundation of the United States to protect human rights and to promote democracy worldwide."

The Chinese dissident declined to give information on his personal situation in the United States, saying only he intended to hold a further news conference in Washington on October 2.