A bipartisan group of US senators Tuesday urged President Barack Obama to highlight human rights concerns when his Chinese counterpart Xi Jinping visits next month, in particular Beijing's "extraordinary assault" on rule of law.

"We urge you to make human rights and political reform in China a key and public component of the agenda for your discussions," wrote the lawmakers, including Senate Armed Services Committee chairman John McCain, ranking Senate Foreign Relations Committee Democrat Ben Cardin, and number two Senate Republican John Cornyn.

The lawmakers, five Democrats and five Republicans, acknowledged the agenda for the talks will be packed with issues like economics and trade, China's recent actions in the East and South China Seas, climate change and cyber-security.

But they stressed that human rights have suffered from a crackdown in China, where they say that the government has "tightened its controls" on free expression, including restrictions on media, academia and the Internet.

"Under President Xi, there has been an extraordinary assault on rule of law and civil society in China," the senators warned, citing as an example the detention or harrassment of more than 250 lawyers and political activists since July 9.

They also urged Obama to press Xi to immediately release imprisoned Nobel Peace Prize recipient Liu Xiaobo and end the "illegal" house arrest of his wife; refrain from persecuting those who practice their religion, including Falun Gong practitioners; and refrain from interfering in the traditional system of recognizing Tibetan Buddhist lamas.

"We know you share these concerns," the senators wrote Obama.

None of the five US senators currently running for president -- Republicans Ted Cruz, Lindsey Graham, Rand Paul or Marco Rubio, and independent Bernie Sanders running for the Democratic nomination -- signed the letter.

Xi is also general secretary of China's Communist Party. He has visited the United States before, but never on an official state visit.