US President Donald Trump has signed what he called a "seriously flawed" bill imposing new sanctions on Russia, pressured by his Republican Party not to move on his own towards a warmer relationship with Moscow in light of Russian actions.
The legislation is aimed at punishing Moscow for interfering in the 2016 US presidential election and for its military aggression in Ukraine and Syria, where the Kremlin has backed President Bashar Assad.
The law also imposes financial sanctions against Iran and North Korea.
Mr Trump said the law will "punish and deter bad behaviour by the rogue regimes in Tehran and Pyongyang" and enhance existing sanctions on Moscow.
The president had been reluctant to proceed with the bill, even after it was revised to include some changes that American and European companies sought to ensure that business deals were not stifled by new sanctions.
Mr Trump has expressed frustration over Congress's ability to limit or override the power of the White House on national security matters, saying that it is complicating efforts to co-ordinate with allies - a sentiment he expressed in Wednesday's statement.
Last week, the House overwhelmingly backed the bill, 419-3, and the Senate rapidly followed its lead with a 98-2 vote.
Those margins guaranteed that Congress would be able to beat back any attempt by Mr Trump to veto the measure.
The president said that he signed the bill "for the sake of national unity".
"The bill remains seriously flawed - particularly because it encroaches on the executive branch's authority to negotiate," Mr Trump said.
"By limiting the executive's flexibility, this bill makes it harder for the United States to strike good deals for the American people, and will drive China, Russia, and North Korea much closer together."
Mr Trump's talk of extending a hand of co-operation to Russian President Vladimir Putin has been met with resistance as sceptical politicians look to limit his leeway.
The new measure targets Russia's energy sector as part of legislation that prevents Mr Trump from easing sanctions on Moscow without congressional approval.
Those limits, backed by Republicans as well as Democrats, resulted from politicians' worries that Mr Trump might ease the financial hits without first securing concessions from Mr Putin.
Republicans refused to budge even after the White House complained that the "congressional review" infringed on Mr Trump's executive authority.
Moscow responded to a White House announcement last week that Mr Trump intended to sign the bill, ordering a reduction in the number of US diplomats in Russia.
Top members of Mr Trump's administration voiced their unhappiness with the bill anew this week, echoing his sentiments that it poses more diplomatic hindrances than solutions.
"Neither the president nor I are very happy about that," secretary of state Rex Tillerson said on Tuesday of the sanctions bill, which he had urged politicians not to approve.
"We were clear that we didn't think that was going to be helpful to our efforts, but that's the decision they made," he said.
Mr Tillerson conceded that he is unable to show that the US has fulfilled Mr Trump's objective of a new, more co-operative relationship between the former Cold War foes, noting only modest efforts in Syria as a sign the nations share some common goals.
While he said Americans want the US to get along with the nuclear-armed power, he did not address other concerns at home.
US intelligence agencies have accused Moscow of meddling in the 2016 presidential election to help Mr Trump.
"The situation is bad, but believe me - it can get worse," Mr Tillerson said.
Vice President Mike Pence, travelling on Tuesday in the former Soviet republic of Georgia, sought to reframe the sanctions as a "further sign of our commitment" to counter Russian aggression in the region.
"The president and our Congress are unified in our message to Russia: A better relationship, the lifting of sanctions will require Russia to reverse the actions that caused the sanctions to be imposed in the first place," Mr Pence said.
"And not before."
Politicians on both sides of the aisle celebrated the passage of the sanctions bill.
"It's long overdue," Democratic Senator Mark Warner, vice chairman of the Senate intelligence committee, said of Mr Trump's decision to sign the bill nearly a week after it cleared Congress.
"Hope we'll send again a strong message to Russia that we can't have interference in our elections going forward."
Republican Senator Bob Corker, chairman of the Foreign Relations Committee, said he had not read the statement Mr Trump issued announcing that he had signed the sanctions bill.
But Mr Corker, who shepherded the legislation through the Senate, appeared indifferent to Mr Trump's criticisms.
"Somebody pointed it out," Mr Corker said, exiting the Senate chamber after a vote. "That's fine."