A group of US Republican senators have urged the Treasury Department to significantly tighten the financial screws on North Korea to curb its dangerously accelerating nuclear and missile programs.

The six senators -- Ted Cruz, Cory Gardner, Thom Tillis, Marco Rubio, Pat Toomey and David Perdue -- made the appeal in a joint letter urging Treasury Secretary Steven Mnuchin to "execute the full extent of financial sanctions and targeted financial measures provided for under current law."

"As (North Korean leader) Kim Jong-un has exposed his willingness to increase ballistic missile testing with the ultimate goal of achieving nuclear breakout, the potential for this regime to attain a developed and capable intercontinental ballistic missile poses an imminent threat that cannot be ignored," they said in the letter sent Tuesday.

"North Korea's test of an intermediate-range ballistic missile this past weekend demonstrates advancement in fuel and launch technology, underscoring the necessity of faithfully executing the law to meet this growing threat," the senators said.

They called for blacklisting any remaining North Korean banks so as to cut off the regime from the international financial system; exposing the North's money laundering network; investigating whether the North merits designation as a state sponsor of terrorism; and investigating the Bank of China and 12 Chinese banks for possible violations of US laws or regulations in connection with the North.

The North carried out the missile launch on Sunday morning in the first provocative act by Pyongyang since the inauguration of US President Donald Trump. The launch came after North Korean leader Kim Jong-un threatened to test-fire an intercontinental ballistic missile apparently capable of reaching the US.

On Monday, the North said the launch represented a successful test of a newly developed intermediate-range missile powered by solid fuel. Weapons experts say solid-fuel missiles pose greater threats as they require less preparation time than liquid-fueled rockets, and can be fired from mobile launchers easy to move around. (Yonhap)