WASHINGTON -- A bipartisan group of US senators Wednesday warned North Korea of further economic sanctions in response to any provocation, such as a long-range missile test.

The four senators -- Chris Van Hollen (D-MD), Pat Toomey (R-PA), Sherrod Brown (D-OH) and Rob Portman (R-OH) -- led passage of a North Korea sanctions bill as part of an annual defense policy bill that passed the Senate on Tuesday.

The defense bill is certain to be enacted into law as US President Donald Trump said last week he will sign it "immediately."

The sanctions provision, dubbed the Otto Warmbier North Korea Nuclear Sanctions Act of 2019, mandates sanctions on foreign banks and companies that facilitate illicit financial transactions for the North.

The measure would especially affect Chinese banks.

At a news conference on Capitol Hill, Van Hollen said the bill sends a clear message to Pyongyang at a time when the regime has threatened to give an unwanted "Christmas gift" to Washington in protest of their stalled denuclearization negotiations.

Many believe the North could test an intercontinental ballistic missile unless the US offers concessions before the year-end deadline set by Pyongyang.

"I think, regardless of what their thinking is, we're here together because we think it's important to send a very clear message that we are going to respond to North Korean aggression by further ratcheting up economic pressure," Van Hollen said.

And the bill's passage is timely, he said, because China and Russia this week proposed a draft United Nations resolution calling for the lifting of some UN sanctions on the North.

"China has looked the other way while their banks and businesses, in many instances, have continued to do business with the North Korean regime," the senator continued. "Rather than easing sanctions and relieving the pressure on North Korea to come to the negotiating table in good faith to denuclearize the Korean Peninsula, we need to put teeth in the existing very leaky sanctions regime, and that's exactly what this legislation does."

Standing alongside the senators were Fred and Cindy Warmbier, whose college student son, Otto, died in 2017 after more than a year of detention in the North.

The Warmbiers have accused the North Korean regime of torturing their son and causing him to fall into a coma.

"I am still traumatized by what North Korea did to our family, and certainly what they did to our son," Fred Warmbier said. "Today I'm overjoyed at the commitment that these senators have put in their efforts to make a difference in North Korea."

He said he believes the sanctions bill will be a tool to force North Korea to engage with the outside world over its illegal activities and ultimately change its behavior.

Cindy Warmbier had a message for North Korea.

"People matter. Otto matters," she said. "We're never going to let you forget our son." (Yonhap)