WASHINGTON (Reuters) - US President Donald Trump said on Thursday he wanted Ukraine and China to investigate the activities of his political rival Joe Biden, his former vice president and son.

A telephone call on July 25, released by the White House, revealed that Trump had pressed his Ukrainian counterpart Volodymyr Zelinsky to open an investigation into the activities of Biden and his son Hunter.

The revelation came after a complaint from an informant who claimed that Trump had withheld US aid to Kiev to pressure the Ukrainian president to heed his request.

"I recommend that they open an investigation into Biden and his son," Trump said in response to a question about what Zielinski wants to do.

As he left the White House to visit Florida, Trump said he believed China should also open an investigation into Monday's activities, hinting at unconfirmed allegations made by him and his lawyer about Hunter Biden's dealings in China.

"By the way, China should also launch an investigation into Biden and his son because what happened in China is as bad as in Ukraine," Bush said.

Asked if he intended to ask China to intervene, Trump replied: "It's certainly something we can start thinking about."

In a preliminary reaction, the chairman of the House Intelligence Committee, Adam Schiff, considered Trump's remarks as an essential reckless oath.