WASHINGTON, Feb 14 (Reuters) - U.S. lawmakers, including some leading Republicans, called on Tuesday for a deeper inquiry into former national security adviser Michael Flynn's ties to Russia, after he was forced out in President Donald Trump's biggest staff upheaval so far.
Flynn quit on Monday after only three weeks in the job amid revelations that he had discussed U.S. sanctions on Russia with the Russian ambassador to the United States before Trump took office, in a potentially illegal action, and had later misled Vice President Mike Pence about the conversations.
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Trump asked for Flynn's resignation and Flynn offered it to him, a senior White House official said.
His departure was another drama for an administration already repeatedly distracted by miscues and internal dramas since the Republican president took office on Jan. 20.
Transcripts of intercepted communications, described by U.S. officials, showed that the issue of U.S. sanctions came up in conversations between Flynn and the ambassador in late December.
The conversations took place around the time that then President Barack Obama was imposing sanctions on Russia after charging that Moscow had used cyber attacks to try to influence the 2016 presidential election in Trump's favor.
Flynn, a retired Army general and former U.S. intelligence official, quit hours after a report saying the Justice Department had warned the White House weeks ago that he could be vulnerable to blackmail over his conversations with Ambassador Sergei Kislyak.
Democrats, who do not have control of Congress, clamored for more action over Flynn.
"The American people deserve to know at whose direction Gen. Flynn was acting when he made these calls, and why the White House waited until these reports were public to take action," Democrat Mark Warner, the Senate intelligence committee's vice chairman, said in a statement.
Two leading Republicans in the Senate, Bob Corker and John Cornyn, also said the intelligence committee should investigate Flynn's contacts Russia and that he may need to testify.
Republican Senator Roy Blunt, a member of the same committee, told a St. Louis radio station that the panel should interview Flynn "very soon" as part of its investigation into attempts by Russia to influence the U.S. election.
But the highest-ranking Republican in Congress, House of Representatives Speaker Paul Ryan, sidestepped questions about whether lawmakers should look into Flynn's Russia ties, adding he would leave it to the Trump administration to explain the circumstances behind Flynn's departure.
Flynn, an early and enthusiastic supporter of Trump, was a strong advocate of a softer line toward Russian President Vladimir Putin and his departure from the key post could hinder Trump's efforts to warm up relations with Moscow.
"General Flynn's resignation also raises further questions about the Trump administration's intentions toward Vladimir Putin's Russia," said Senator John McCain, a leading Republican voice on foreign relations.
LEAKS WORRY TRUMP
The Washington Post reported last week that the issue of sanctions came up in the conversations with the ambassador, although Flynn told Pence that they had not.
Democratic Senator Chris Coons asked why Flynn was allowed to remain in his post for so long after the White House was warned of the potential for blackmail. "This isn't just about what happened with General Flynn," Coons told MSNBC. "What did President Trump know? What did the president know and when did he know it?" Coons said.
In his first public comment about the Flynn issue since the resignation, Trump deflected the focus to leaks from his administration. "The real story here is why are there so many illegal leaks coming out of Washington? Will these leaks be happening as I deal on N.Korea etc?' he wrote on Twitter.
In his resignation letter, Flynn acknowledged he had "inadvertently briefed the vice president-elect and others with incomplete information regarding my phone calls with the Russian ambassador."
A U.S. official familiar with the transcripts of the calls with Kislyak said Flynn indicated that if Russia did not retaliate in kind for Obama's Dec. 29 order expelling 35 Russian suspected spies and sanctioning of Russian spy agencies, that restraint could smooth the way toward a broader discussion of improving U.S.-Russian relations once Trump took power.
To the surprise of some observers at the time, Putin did not take retaliatory measures. Trump praised his restraint.
Flynn's discussions with the Russian diplomat could potentially have been in violation of a law known as the Logan Act, banning private citizens from negotiating with foreign governments about disputes or controversies with the United States. However, nobody has been prosecuted in modern times under the law, which dates from 1799.
Vice Admiral Robert Harward, who served under Defense Secretary James Mattis, is the leading candidate to replace Flynn, two U.S. officials said on Tuesday.
The scramble to replace Flynn began on Monday evening and continued with phone calls and meetings into the early hours of Tuesday in an effort to enable Trump to make a decision and put the matter behind him as soon as possible, said an official involved in the effort.
Also under consideration was retired General David Petraeus, a former CIA director whose reputation was tainted by a scandal over mishandling classified information with his biographer, with whom he was having an affair.
(Additional reporting by Susan Cornwell, John Walcott, Doina Chiacu and Susan Heavey; Writing by Doina Chiacu and Alistair Bell; Editing by Frances Kerry)