WASHINGTON (Reuters) - Roger Stone, a veteran Republican operative, said on Wednesday that he will not appear to answer questions before two U.S. Senate committees about his ties to and support of Donald Trump when he was running for president in 2016.

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A long-time Trump associate, Stone has been involved in inquiries into Russian meddling in the 2016 U.S. presidential election, any collusion between Moscow and the Trump campaign and possible obstruction of justice.

In declining to talk to the Senate panels, Stone invoked the Fifth Amendment of the U.S. Constitution, which gives witnesses the right to refuse to testify if they believe such testimony would incriminate them.

At this point, the Senate Judiciary and Intelligence Committees have not subpoenaed Stone. Both panels had asked him to produce documents and talk to committee investigators.

Stone, whose public explanation of his activities in 2016 has shifted over time, and his lawyer Grant Smith told Reuters that Stone has declined the committees’ requests.

In September 2016, Stone did attend a private meeting of the Intelligence Committee of the U.S. House of Representatives. Only his account of his testimony there has been made public.

Stone and his lawyer have said that they have not been approached by Special Counsel Robert Mueller, who is also investigating Russian political interference. Moscow has denied meddling in U.S. elections.

During the 2016 campaign, Stone issued tweets implying that he had inside knowledge of data in the possession of hackers that could embarrass Democratic presidential nominee Hillary Clinton, then Trump’s rival, and other Democrats.

Stone’s best-known tweet, of Aug. 21, 2016, said, “Trust me, it will soon the Podesta’s time in the barrel. #CrookedHillary”.

Senator Dianne Feinstein, the senior Democrat on the Judiciary Committee, had asked Stone to turn over documents or communications on his attempts in 2016 to obtain data hacked from computers used by Clinton and other leading Democrats, including her senior campaign adviser John Podesta.

Feinstein also had asked for any communications between Stone and WikiLeaks, its founder Julian Assange and a hacker who called himself Guccifer 2.0, whom U.S. agencies have said was an operative for Russian military intelligence.

Stone now says he never had any advance access to hacked materials. In an email to Reuters, he said his testimony to the House panel was “entirely truthful and accurate.

He said in the email, “If any member of the house intelligence committee has evidence of Russian collusion or wiki leaks collaboration or can prove that I received anything whatsoever from WikiLeaks including allegedly stolen or allegedly hacked emails I challenge them to produce it, otherwise stop playing ridiculous word games.”