WASHINGTON (REUTERS) - Frustrated US lawmakers called on Tuesday (Sept 12) for a "supercharged" response to North Korea's nuclear tests, saying Washington should act alone if necessary to stiffen sanctions on companies from China and any country doing business with Pyongyang.

"I believe the response from the United States and our allies should be supercharged," said Representative Ed Royce, chairman of the House of Representatives Foreign Affairs Committee.

"We need to use every ounce of leverage... to put maximum pressure on this rogue regime," he told a hearing on North Korea.

"Time is running out."

The UN Security Council stepped up sanctions on Monday following Pyongyang's sixth nuclear test on Sept 3, imposing a ban on textile exports and capping oil imports.

It was the ninth sanctions resolution unanimously adopted by the council since 2006 over North Korea's ballistic missile and nuclear programmes. To win Chinese and Russian support, Washington dropped demands including a bid for an oil embargo.

Committee members expressed frustration that previous sanctions had not deterred Pyongyang.

"We've been played by the Kims for years," Republican Representative Ted Poe said, referring to North Korean leader Kim Jong Un and his predecessors.

Royce said Washington did not need Beijing's cooperation to increase pressure on North Korea.

"It's been a long, long time of waiting for China to comply with the sanctions that we pass and, frankly, with the sanctions that the United Nations passed," he said.

Lawmakers pressed State and Treasury Department officials for evidence new sanctions would be more effective.

Some praised President Donald Trump's administration for threatening a military response, while others were critical, insisting that should be a last resort.

"It's hard to overstate just how devastating a conflict on the Korean peninsula would be," said Representative Eliot Engel, the committee's top Democrat.

Assistant Treasury Secretary Marshall Billingslea acknowledged he had not seen sufficient evidence past sanctions were effective, but defended the administration's strategy.

Billingslea called on anyone aware of efforts to enable North Korean trade to come forward before getting caught.

"We are closing in on North Korea's trade representatives," he said.

"We can designate Chinese banks and companies unilaterally, giving them a choice between doing business with North Korea or the United States," said Royce, who had breakfast on Tuesday with Secretary of State Rex Tillerson.

"We should go after banks and companies in other countries that do business with North Korea the same way," he said.