(Adds context, White House reaction, details)
WASHINGTON, July 27 (Reuters) - U.S. President Donald Trump could veto pending legislation which would slap new sanctions on Russia, in order to push for a tougher deal, a top White House aide said on Thursday.
Russia has warned it could retaliate if the legislation is passed, and the European Union said the new sanctions might affect its energy security and prompt it to act, too.
The White House has said Trump is still evaluating the bill and supported strong sanctions against Russia, though tougher sanctions would likely strain the relationship with Moscow which Trump had been seeking to improve.
"He may sign the sanctions exactly the way they are or he may veto the sanctions and negotiate an even tougher deal against the Russians," White House Communications Director Anthony Scaramucci told CNN.
On Wednesday, U.S. lawmakers reached an agreement, clearing the way for the Senate to pass a measure as soon as this week to impose new sanctions on Russia and bar the president from easing sanctions on Moscow if Congress objects.
The bill, which also includes sanctions on Iran and North Korea, has enough bipartisan support that lawmakers could easily override the threatened veto.
There was no immediate word on when the Senate would vote but members of both parties have said they want to send it to Trump before they leave Washington mid-month for their summer recess.
Senate Democratic Leader Charles Schumer said Democrats would work with Republicans to move the bill quickly, adding that Congress would swiftly override if Trump were to veto the measure.
Trump's fellow Republicans as well as Democrats have pushed for more sanctions partly as a response to findings by U.S. intelligence agencies that the Kremlin interfered in the 2016 U.S. election to boost Trump's campaign.
Several congressional committees and a federal special counsel are investigating possible collusion between Moscow and Trump's campaign, something both Trump and the Kremlin deny.
The House of Representatives has already approved the sanctions. If passed by the Senate as expected, the bill would be sent to the White House for Trump to sign or veto.
However, Trump can impose new sanctions on Russia at any time through an executive order.
Lawmakers said the administration had spent weeks lobbying for a weaker bill. Trump's concerns include a provision letting Congress stop any effort to ease existing sanctions on Russia.
A former U.S. government official was skeptical the White House wanted to strengthen the bill.
Toughening the bill, I cannot believe, said the former official, who spoke on condition of anonymity.
I can understand why they would want to weaken it because it is intended to (constrain) the presidents ability to unilaterally remove sanctions. It is a rebuke to him. It is a rebuke to Trump because of his flirtation with (Russian President Vladimir) Putin, the former official added.
The bill would affect a range of Russian industries and might further hurt the Russian economy, already weakened by 2014 sanctions imposed after the Ukraine crisis.
An adviser to Russian Putin told Reuters that any tightening of the sanctions should not have a deeper impact but hope they would be lifted has faded.
The White House's rhetoric on the sanctions bill echoes that surrounding the president's controversial decision to withdraw the United States from the Paris Climate Agreement, which includes 194 countries.
On May 31, Trump said the United States would no longer participate in the landmark 2015 global climate change agreement and that his administration would begin negotiations either to re-enter the Paris accord or to have a new agreement "on terms that are fair to the United States".
But other world leaders said a new agreement was not an option. French President Emmanuel Macron told Trump the deal could not be renegotiated.
(Additional reporting by Susan Heavey, Eric Walsh, Rick Cowan, Valerie Volcovici, Roberta Rampton and Arshad Mohammed; Writing by Yara Bayoumy; Editing by Jeffrey Benkoe and James Dalgleish)