The lawyer, Jay Sekulow, contended the tweet was not a confirmation of the investigation, but instead a response to a report in The Washington Post
"That tweet was in response to a Washington Post story that ran with five unnamed sources," Sekulow said in an interview that aired Sunday on CNN's "State of the Union."
Trump tweeted on Friday: "I am being investigated for firing the FBI Director by the man who told me to fire the FBI Director! Witch Hunt"
The Washington Post story cited
five officials who had been briefed on interview requests from special counsel Robert Mueller with three top intelligence officials to see if Trump had attempted to obstruct justice.
Trump's tweets following the report appeared to confirm the investigation, but his lawyer said it only appeared that way because of the character limit on Twitter. Sekulow added that Trump is "very effective" with his use of social media.
"There's a limitation on Twitter, as we all know," Sekulow said. "The President's response was as it related to the Washington Post report. He cannot in a Twitter statement include all of that in there. ... That's it. Simple explanation."
Sekulow stressed repeatedly that Trump is not under investigation.
A source familiar with the matter told CNN's Evan Perez that investigators for Mueller would speak
with Director of National Intelligence Dan Coats and National Security Agency Director Mike Rogers. The source said investigators have sought information from Richard Ledgett, who recently retired as deputy NSA director and, the source said, had written a memo documenting an attempt from Trump urging Rogers to tamp down on the FBI's Russia investigation.
Both Coats and Rogers declined
before the Senate intelligence committee earlier this month to answer questions about their conversations with Trump, but both said they had never felt urged by Trump to intervene in the Russia probes.
Former FBI Director James Comey told the
Senate intelligence committee that Trump pressured him on the Russia investigation and asked him to drop an investigation into former national security adviser Michael Flynn.
Trump has denied
making these comments, which Comey said he documented in contemporaneous memos.
Deputy Attorney General Rod Rosenstein appointed Mueller as special counsel following Comey's ouster in early May. Mueller was tasked with taking over the executive branch's investigation into alleged Russian interference and potential collusion between Russia and Trump's associates.
Comey made the existence of this investigation public in a March hearing before the House intelligence committee.
Rosenstein, in an appearance before Congress on Tuesday, declined to answer
a question about his memo recommending Comey's firing by saying it could be part of the special counsel's investigation.