Norwegian Prime Minister Erna Solberg on Friday came down heavily on the increasing trade protectionist measures by U.S. President Donald Trump's administration, warning they might lead to "regression, war and conflict."

"A global trade war and increasing protectionism are the last thing the world needs now," Solberg said at her Conservative Party's annual national conference in Gardermoen, north of Oslo.

The concern came after the United States unilaterally decided to levy massive tariffs on Chinese products, aiming to start a trade war.

Earlier this week, the U.S. Trade Representative (USTR) proposed to impose an additional 25 percent tariff on US$50 billion of imports from China. It was followed by Trump saying on Thursday that he has asked the USTR to consider slapping additional tariffs on Chinese products worth US$100 billion.

Solberg said the United States appeared to be "the biggest threat" to free trade while China was acting like one of the "foremost defenders".

Trade and cooperation are important not only for countries trying to lift their populations out of poverty, but also for developed countries like Norway, because trade protectionism will make it harder to achieve sustainable goals, she said.

"Norway is going to be a driving force for ongoing free and fair world trade," she said, warning that "historically, periods of extensive protectionism have led to regression, war and conflict."

On March 23, Norway asked the United States to respect the rules of the World Trade Organization as it fell under new U.S. tariffs on steel and aluminum.

The Trump administration last month imposed a 25-percent tariff on imported steel and a 10-percent tariff on imported aluminum, triggering criticism and outrage from around the world.