WASHINGTON -  US President Trump, in a series of tweets Saturday, responded to the mounting questions over his ties to Russia by accusing then-President Obama of wiretapping him at Trump Tower in New York just before the November election.

The unsubstantiated claim follows several days of stories raising questions about meetings between members of the Trump campaign and Russian officials, particularly two previously undisclosed meetings between now Attorney General Jeff Sessions and Russian ambassador Sergei Kislyak.

“How low has President Obama gone to tapp [sic] my phones during the very sacred election process,” Trump wrote. “This is Nixon/Watergate. Bad (or sick) guy!”

In making the charges, Trump did not elaborate on provide any evidence backing up the explosive accusation. Ben Rhodes, Obama’s foreign policy adviser, responded to Trump to tweets, first stating that “No President can order a wiretap. Those restrictions were put in place to protect citizens from people like you.”

The tweet blasts began early this morning, from the Winter White House at Mar-a-Lago in Florida when Trump raised the Sessions issue by noting the first meeting between the senator from Alabama and the Russian ambassador was set up by the Obama administration as part of an education programme.

Eight minutes later, he raised the charge of illegal surveillance by the Obama administration: “Terrible! Just found out that Obama had my “wires tapped” in Trump Tower just before the victory. Nothing found. This is McCarthyism!”Then: “Is it legal for a sitting President to be “wire tapping” a race for president prior to an election? Turned down by court earlier. A NEW LOW!”And: “I’d bet a good lawyer could make a great case out of the fact that President Obama was tapping my phones in October, just prior to Election!” To that, Rhodes responded: “No. They couldn’t. Only a liar could do that.”

Meanwhile, a spokesman said Saturday that Obama never ordered surveillance on any American citizen.

“President Obama nor any White House official ever ordered surveillance on any US citizen,” Obama spokesman Kevin Lewis said in a one-line statement.

Sessions recused himself from any Trump-Russia investigation after the Justice Department acknowledged he spoke twice with the Russian ambassador last year and failed to disclose the contacts during his Senate confirmation process. Sessions said he did not tried to mislead anyone but could have been more careful in his answers. He planned to file amended testimony Monday, a Justice Department spokesman said.

The president responded to the Sessions issue obliquely Friday by taking a swing at Senate Minority Leader Charles Schumer, a Democrat, noting the New York senator previously met with Russian President Vladimir Putin.

In a tweet, Trump posted a photo of Schumer with Putin during the Russian leader’s visit to New York in 2003. He demanded an investigation of “close ties” between Schumer, House Minority Leader Nancy Pelosi and Russia and “lying about it.”He called Schumer, who has demanded Sessions’ resignation, a “total hypocrite.”

Trump’s Saturday morning tweets come less than a day after radio talk show host Rush Limbaugh accused Obama of executing a “silent coup” to unseat Trump and render him “effectively immaterial” as president.”The real Russian scandal is the collusion between Barack Obama and his administration and the Russians,” Limbaugh said.

“Obama’s team used the pretext of Russian interference in the election to justify wiretaps and illegal leaks of the Trump team, including a US senator and now attorney general.”By late morning, Trump had - at least temporarily - moved on, saying Arnold Schwarzenegger, his replacement on NBC’s “Celebrity Apprentice” did not voluntarily leave the show but “was fired by his bad (pathetic) ratings, not by me.” He called it a “Sad end to a great show.

“The movie star and former California governor announced Friday he was leaving the show after one season. He told Empire magazine that he would decline to return, even if asked. Trump, who has remained executive producer of the show, has mocked the show’s sagging ratings.

“With Trump being involved in the show, people have a bad taste and don’t want to participate as a spectator or sponsor or in any other way support the show,” Schwarzenegger said. “It’s a very divisive period right now and I think the show got caught up in all that division.”