In an interview given to Fox News on Wednesday, President Donald Trump defended unsubstantiated accusations made by him against former President Barack Obama, through Twitter earlier this month. In the interview, Trump said that “wiretap covers a lot of different things,” while reiterating his claim that the former president ordered the wiretapping of Trump Tower in New York.

Commenting for the first time since making the explosive and controversial accusation on March 4, Trump referenced two media reports — a New York Times article and a story by Fox News host Bret Baier— as his possible sources for the allegations, while speaking with Fox News host Tucker Carlson.

"Well, I've been reading about things. I read in, I think it was Jan. 20, a New York Times article where they were talking about wiretapping. There was an article, I think they used that exact term. … I said, wait a minute, there's a lot of wiretapping being talked about," Trump said according to the Hill.  The NYT article Trump mentioned did not say that Obama wiretapped him.

Trump also suggested that he may produce some proof or evidence about his claims.

“I think you’re going to find some very interesting items coming to the forefront over the next two weeks. … We will be submitting certain things and I will be perhaps speaking about this next week. But it's right now before the committee and I think I want to leave it there," Trump added.

Trump’s comments on the subject came as bipartisan support demanding proof for his wiretapping claims begins to grow. On Wednesday, two senators — Lindsey Graham (R-South Carolina) and Charles E. Grassley (R-Iowa) — threatened to block the nomination of Rod J. Rosenstein as deputy attorney general until the FBI submitted evidence about the president’s claim.

Sen. Graham also threatened to issue a subpoena if the FBI didn’t fall in line, putting pressure on bureau director James Comey.

"I want to get to the bottom of it. The FBI would know if a warrant was issued. They would know if a warrant was applied for. I want to answer that question," he said. "If they do not provide the answer to that letter we wrote in a bipartisan fashion, there will be a bipartisan subpoena following the FBI," he told CNN.

Attorney General Jeff Sessions also told reporters Wednesday he never gave Trump any reason to believe he had been wiretapped by the Obama administration during the campaign.

The Republican chairman of the House Intelligence Committee, Representative Devin Nunes of California also said he had seen no evidence backing up Trump’s allegation.

“We don't have any evidence that that took place,” Nunes told reporters at a news conference in Washington. “I don't think there was an actual tap of Trump Tower.”

“Are you going to take the tweets literally? And if you are, then clearly the president was wrong,” he added while saying that hearings of the intelligence committee open Monday.