South Korea and the United States claimed the sole goal of THAAD is to guard against North Korean missiles.
Separately, Trump's national security adviser, Army Lt. Gen. H.R. McMaster, said North Korea's most recent missile test represents "open defiance of the worldwide community".
In a phone call to South Korea's national security chief Kim Kwan Jin, National Security Adviser H.R. McMaster said the US would honor a 2016 pact between the two countries requiring the U.S.to bear the cost of the system, meant to protect against a North Korean missile attack.
President Donald Trump has been asked about the failure of several North Korean missile tests recently and why those launches keep blowing up.
Vice President Mike Pence reaffirmed the USA commitment to South Korea's security but said on NBC that Trump would "continue to call on the prosperous nations that the United States provides security and protection for to do more in their own defence".
"And I can tell you also, I don't believe that the president of China, who is a very respected man, will be happy either", Trump said.
Last month, controversy erupted after a USA aircraft carrier strike group was found to have not been heading to the peninsula as Trump and his top aides had said it was. US Secretary of State Rex Tillerson said Friday that Washington was open to talks with North Korea about denuclearization, a tactic China has called for for some time. "I mean, we'll see".
The remarks stunned Seoul, with South Korean politicians immediately rejecting his push for payment for the Terminal High Altitude Area Defence (Thaad) battery. About 300 protesters faced off against 800 police officers and succeeded in blocking two U.S. Army oil trucks from entering the site, South Korean media reported.
Sen. Ben Cardin, a senior member of the Senate Foreign Relations Committee, also urged Trump not to "divide" the alliance with the South at a time when tensions with North Korea are escalating.
The U.S. aircraft carrier USS Carl Vinson transits the Sunda Strait, Indonesia. "It's a billion-dollar system", he said. They participated in a day of solidarity with around 5,000 local villagers and members of the Won Buddhist community, who are actively resisting the deployment of the U.S. missile defence system in their locality.
McMaster was responding to the controversy Trump stirred up last week with South Korea, a key USA ally in Asia.
At a National Assembly Steering Committee plenary session last July, Kim fielded a question from Justice Party lawmaker Roh Hoe-chan on whether there was a chance THAAD deployment costs could be included in South Korea's share of defense expenses.
In the Reuters interview Trump also threatened to renegotiate or end what he called a "horrible" trade deal with South Korea.