WASHINGTON: US Secretary of State Mike Pompeo on Tuesday asked Washington's think tanks to disclose foreign funding, warning of Chinese and Russian backing for the institutions known for wide influence on US policy.

Washington's think tanks have for decades served as homes in waiting for US experts when they are out of government and most aggressively seek funding - although foreign money is most likely to come from nations friendly to the United States.

Pompeo called on think tanks that seek to cooperate with the State Department to disclose "prominently" on their websites any foreign funding, including by state-supported entities.

"Disclosure is not a requirement for engaging with such entities. Department staff will, however, be mindful of whether disclosure has been made and of specific funding sources that are disclosed when determining whether and how to engage," Pompeo said in a statement.

"We hope one day soon that US efforts to promote free and open dialogue about economic and personal liberty, equal citizenship, the rule of law and authentic civil society will be possible in places such as China and Russia."

President Donald Trump's administration has in recent months ramped up pressure on China, with Pompeo taking particular aim at its sources of influence in the United States.