(Adds Trump comments, background)

WASHINGTON, April 5 (Reuters) - President Donald Trump said on Thursday he had instructed U.S. trade officials to consider $100 billion in additional tariffs on China, fueling an already heated trade dispute between the world's two biggest economies.

Trump said in a statement the further tariffs were being considered "in light of China's unfair retaliation" against earlier U.S. trade actions that included $50 billion of tariffs on Chinese goods.

He added that the U.S. Trade Representative had determined that China "has repeatedly engaged in practices to unfairly obtain America’s intellectual property."

U.S. stock index futures fell in reaction to Trump's latest statement. Financial markets have swung wildly over the past few days in response to fears of escalating trade tensions between Washington and Beijing.

"Rather than remedy its misconduct, China has chosen to harm our farmers and manufacturers," Trump said.

The tariffs are aimed at forcing changes to Chinese government policies aimed at transferring U.S. intellectual property to Chinese companies.

The USTR's "Section 301" investigation authorizing the tariffs alleges China has systematically sought to misappropriate U.S. intellectual property through joint venture requirements that often cannot be negotiated without technology transfers, something China denies.

The tariffs have stirred fears that the two countries will spiral into a trade war that will crush global growth.

The Trump administration this week proposed 25 percent tariffs on some 1,300 Chinese industrial and other products. China shot back with a list of similar duties on American imports including soybeans, planes, cars, beef and chemicals.

The retaliatory tariffs have left Republican lawmakers from Western and Midwestern states fearful of a big hit to U.S. farming exporters.

(Reporting by Eric Beech and Caren Bohan in Washington; Editing by Peter Cooney)