U.S. officials Tuesday warned they will boost pressure on North Korea with new economic penalties after the cyber-attack on Sony, but said Washington was open to engagement with the rogue state.

President Barack Obama slapped sanctions on North Korea early this month in retaliation for the hacking of Hollywood studio Sony Pictures' computer network.

U.S. officials have blamed the attack on Pyongyang and described it as the most damaging commercial hack in U.S. history, costing the Hollywood studio hundreds of millions of dollars.

A U.S. Treasury official told lawmakers at a hearing on confronting North Korea's cyber threat to expect more punishments against the "brazen and isolated regime" in addition to existing sanctions.

"While this increased isolation has made targeting the DPRK more complex, Treasury has continued to use its sanctions authorities to ratchet up the pressure on the DPRK," Assistant Treasury Secretary Daniel Glaser told the House Foreign Affairs Committee.

"As for now, the DPRK remains defiant, continuing its well-documented illicit activities. As long as this is the case, Treasury will continue to deploy the tools at its disposal to raise the financial cost of such behavior and induce the government of the DPRK to abide by its international obligations."

Glaser said the Obama administration would implement the latest executive order on North Korea sanctions, which allows Treasury to impose sanctions on North Korean officials, companies and state organizations including the Reconnaissance General Bureau, the intelligence agency blamed for the Sony attack.

House Republican and committee chairman Ed Royce warned that Washington needs to maintain pressure not just on Pyongyang, but its neighbors and organizations that cooperate with North Korea.

"We need to step up and target those financial institutions in Asia and beyond that are supporting the brutal and dangerous North Korean regime," Royce said.

Royce and the panel's top Democrat, Eliot Engel, said squeezing the country's access to international finance will help target the North Korean regime elite, notably the family of leader Kim Jong-Un.

"The bottom line is, there needs to be an impact on the family that runs the country," Engel said.

But the State Department said that, while North Korea has "consistently rebuffed or ignored" U.S. offers for dialogue, Washington remains prepared to open an avenue of communication.

"We remain open to engagement when possible, but we will continue to apply pressure as needed," Sung Kim, special representative for North Korea policy, told the hearing. (AFP)