WASHINGTON • President Donald Trump has signed an order strengthening a November ban on US investments in alleged Chinese military companies, the White House has said, curbing Chinese access to US capital markets days before he leaves office.

Under the amended directive, by Nov 11, US investors will be required to have completely divested their holdings of securities of companies designated by the Defence Department as owned or controlled by the Chinese military.

The change expands the scope of the initial November executive order, which initially restricted US investors only from buying those securities by that date.

"Today's executive order ensures that the United States retains a key tool to protect US investors from funding Chinese military modernisation," a senior administration official told Reuters on Wednesday.

The executive order is part of Mr Trump's bid to cement his tough-on-China legacy in the waning days of his presidency. It also sought to give teeth to a 1999 law that tasked the Defence Department with drafting a list of Chinese companies it believes are owned or controlled by the Chinese military.

Among the 35 companies that the Defence Department has blacklisted so far are China's top chipmaker SMIC and oil giant CNOOC. But the administration had scrapped plans to blacklist Beijing tech giants Alibaba, Baidu and Tencent.

Washington nonetheless plans to move forward this week with a bid to add as many as nine other Chinese companies to the list, people familiar with the matter said.

Meanwhile, the Trump administration on Wednesday announced an import ban on all cotton and tomato products from western China's Xinjiang region over allegations that they are made with forced labour from detained Uighur Muslims.

The US Customs and Border Protection agency estimates that about US$9 billion (S$11.9 billion) of cotton products and US$10 million worth of tomato products were imported from China into the US in the past year.

The Chinese embassy in Washington said in a statement that the forced labour issue was a "political lie" and vowed to take action to safeguard the rights of its companies.

At a regular briefing yesterday, Chinese Foreign Ministry spokesman Zhao Lijian said: "China opposes politicising economic and trade issues and abusing state power and the concept of national security to suppress foreign companies."

He urged the US to respect market economy principles and provide a fair, unbiased and transparent business environment for foreign companies.

REUTERS, BLOOMBERG