Russia on Wednesday raised the prospect of retaliation after an overwhelming vote by the US House of Representative to impose new sanctions left President Donald Trump facing a tough call.
The sanctions package, which also targets Iran and North Korea, "tightens the screws on our most dangerous adversaries in order to keep Americans safe," House Speaker Paul Ryan said after it passed Tuesday by 419 votes to three.
It now heads to the Senate before Trump faces the tricky choice of whether to veto the bill, which has been opposed by the White House and considerably constrains his ability to lift the penalties.
There is broad support in the Senate for the tougher measures, but debate about whether to include penalties on North Korea.
The legislation is the result of a congressional compromise reached last weekend and is aimed at punishing the Kremlin for allegedly interfering in the 2016 US presidential election and intervening in Ukraine.
European firms working with the Russian energy sector, however, fear that the bill could end up hitting them.
"Under Vladimir Putin, Russia has invaded its neighbour Ukraine, seizing its territory and destabilising its government," House Foreign Affairs Committee chairman Ed Royce said, applauding the bill's passage.
"Left unchecked, Russia is sure to continue its aggression."
- Sanctions 'will not go unanswered' -
Moscow responded angrily to the vote, with deputy foreign minister Sergei Ryabkov insisting Washington had been warned "dozens of times" that any new sanctions would "not go unanswered".
"The authors and sponsors of this bill are taking a very serious step towards destroying the possibilities for normalising relations with Russia," he told state-run TASS news agency.
Key among the provisions is one that handcuffs the US president by complicating any unilateral efforts to ease penalties against Moscow in the future -- effectively placing him under Congress's watch.
Despite initially opposing the bill, Trump appears to have few options in the face of near-total consensus in Congress.
But spokeswoman Sarah Huckabee Sanders said the White House was still "reviewing the House legislation and awaits a final legislative package for the president's desk".
Trump has faced accusations that his administration had sought to reassure Moscow that sanctions imposed by the Obama administration dating back to the Moscow's 2014 annexation of Crimea from Ukraine could be lifted.
The bill also includes fresh sanctions against Iran and its Islamic Revolutionary Guard Corps, which stands accused of supporting terrorism, and North Korea, for its missile tests, are also included in the bill.
Iranian President Hassan Rouhani said Tehran would respond in kind to any breach by the US of the 2015 nuclear deal after the vote.
"If the enemy steps over part of the agreement, we will do the same, and if they step over the entire deal, we will do the same too," Rouhani said at a televised meeting.
The Iranian parliament's national security and foreign affairs committee said it would hold an extraordinary session on Saturday to discuss its response.
- Veto likely not effective -
In mid-June, the Senate voted 98-2 in favour of tough sanctions on Moscow and Tehran, but the text stalled in the House.
With the North Korea sanctions now included, the new measure would need to be passed by the Senate before heading to the White House, likely before summer break begins in mid-August.
Top Senate Democrat Chuck Schumer said he wants the new measure passed and sent to Trump's desk "without delay."
US lawmakers, including Republican leaders, have remained wary of the intentions of the billionaire businessman-turned-president -- who has called for better relations with Moscow -- regarding a relaxation of pressure on Putin.
But even if Trump were to veto the legislation, Congress would likely be able to overcome such a blockage with a two-thirds majority in each chamber.
- European concerns -
From Paris to Berlin, the sanctions bill was seen as a unilateral action by Washington that disrupts a carefully crafted order.
To date, sanctions against Moscow have been coordinated on both sides of the Atlantic, to maintain a united front.
European Union member states were due to meet Wednesday and discuss the issue -- and a possible response.
Several European nations, including Germany, are livid because the new law would allow punishing companies working on pipelines from Russia, for example by limiting their access to US banks.
The provision could theoretically pave the way for sanctions against European partners in Nord Stream 2, a project to build a pipeline carrying Russian gas across the Baltic that could boost supplies to Germany from 2019.
To date, Washington and Brussels had agreed that sanctions would not affect Europe's gas supply.
In an apparent concession, the House modified a provision so the bill only targets pipelines originating in Russia, sparing those that merely pass through, such as the Caspian pipeline that carries oil from Kazakhstan to Europe.