UPDATE 2-Republican chairman says U.S. should do more to hold Russia accountable

accountable@ (Adds comments from Singh, Billingslea, new sanctions)

WASHINGTON, Sept 13 (Reuters) - The Republican chairman of the U.S. House of Representatives Foreign Affairs Committee said on Thursday Washington should do more to hold Moscow accountable for "aggressive acts".

"We cannot expect (Russian President) Vladimir Putin and his corrupt associates to change their behavior in Syria, Ukraine or anywhere else until we prove we will hold them to account," Representative Ed Royce said in his prepared opening statement for a committee hearing on U.S. sanctions policy.

"Those still engaged in significant business with designated Russian individuals and entities need to pay a price," Royce said, as laid out in a sweeping sanctions law the House and Senate passed overwhelmingly in 2017.

The committee's ranking Democrat, Representative Eliot Engel, also said Congress could be doing more.

President Donald Trump has been under pressure, including from his fellow Republicans, to push back harder against Russian meddling in U.S. elections, aggression in Ukraine and involvement in the civil war in Syria.

Assistant Secretary of State Manisha Singh told the committee that Trump administration sanctions have imposed substantial costs on Russia and said they deter "nefarious activities."

Singh said the administration estimates that sanctions have cost the Russian government "tens of billions of dollars."

Trump signed an executive order on Wednesday to strengthen election security, just eight weeks before the Nov. 6 U.S. congressional polls, by slapping sanctions on foreign countries or people who try to interfere in U.S. votes.

Royce said he was also concerned that the U.S. "maximum pressure" policy over North Korea's nuclear program was faltering.

North Korean leader "Kim (Jong Un) appears to be using talks, as he has time and again, to probe for weaknesses and buy time," said Royce. "When our messages are confusing or contradictory, we shouldnt be surprised when others, like Beijing, reportedly resume importing North Korean coal."

Assistant Treasury Secretary Marshall Billingslea said the policy was not faltering. He noted that the administration announced new North Korea sanctions during the hearing.

"We will continue this economic pressure campaign until denuclearization is achieved," Billingslea said.

Billingslea also said the administration will aggressively enforce sanctions it is reimposing on Iran, as Trump rolls back the 2015 nuclear agreement.

Royce said action should be taken against Russian companies and individuals that provide maintenance and other services to Iran's Mahan Air, which the United States has said ferries weapons, fighters and money to Syria. (Reporting by Patricia Zengerle; Editing by Bernadette Baum and James Dalgleish)