A top adviser to former President Barack Obama has labelled reports that she ordered surveillance of Donald Trump's campaign as "absolutely false".
Former National Security Adviser Susan Rice flatly denied she or Mr Obama used intelligence for political purposes.
She was responding to reports alleging she sought to "unmask" any Trump officials who cropped up in foreign surveillance reports.
Ms Rice also rejected claims that she leaked information to US media.
She was pressed on MSNBC about whether she had exposed Mr Trump's former National Security Adviser, Michael Flynn, who was forced to resign in February after misleading the White House about his conversations with the Russian ambassador.
"I leaked nothing to nobody and never have and never would," Ms Rice replied.
She did not say whether she had viewed intelligence reports involving Mr Trump and his aides, citing classified information.
Analysis - Anthony Zurcher, BBC News, Washington
Former Obama National Security Adviser Susan Rice says that while she did request the "unmasking" of some Americans in contact with foreign subjects under government surveillance, she did not do so for "political purposes".
If that's where the story ends, then she was almost certainly legally exercising the broad powers high-level US national security officials have to review reports produced by the intelligence community. There were growing indications that the Russian government was attempting to influence the US presidential election, and a national security adviser would be remiss not to closely inspect any information about possible American involvement.
If, on the other hand, Ms Rice widely disseminated information about US citizens or leaked it to the press, as some Republican critics allege and she adamantly denies, then the picture grows much darker.
The bottom line is that someone, somewhere did reveal details about conversations Michael Flynn, Ms Rice's successor as national security adviser, had with Russian ambassador Sergei Kislyak. That leak, while it revealed that Flynn was being less than truthful with the US public, was illegal.
Rice says this has nothing to do with her. Republican investigators in Congress certainly are unlikely to let the matter end there, however.
Ms Rice has come under intense scrutiny over suggestions she requested the intelligence community to provide the names of Trump administration officials who turned up in surveillance transcripts of foreign subjects.
"The allegation is that somehow Obama administration officials utilised intelligence for political purposes, that is absolutely false," she said.
Ms Rice explained that part of her job as national security adviser was to determine the importance of intelligence reports she received, and sometimes that entailed requesting the identities of those involved.
The US often monitors the communications of foreigners, but the names of any Americans caught up in the dragnet are typically removed from intelligence reports to protect their privacy.
Ms Rice said she could only request the identity of US citizens in spy reports if that helped understand the intelligence better.
But it was the intelligence community that would ultimately determine whether she could access that information, she added.
Ms Rice emphasised that reports of Russian interference in the US election had been"of great concern to all of us on the national security team".
Both the House and Senate intelligence committees and the FBI are investigating alleged Kremlin interference in the US election and whether there is any evidence of collusion between Trump officials and Moscow operatives.
It has also emerged that Russian spies sought to recruit a New York business consultant, Carter Page, as an intelligence source, two years before he joined the Trump campaign as a foreign policy adviser.
The FBI interviewed Mr Page as part of a separate investigation into three Russian men identified as agents of the Russian foreign intelligence agency, the SVR.
Mr Trump denies any ties to Moscow, and has instead alleged that Mr Obama ordered wiretapping of Trump Tower during the presidential election.
When asked about President Trump's unsubstantiated claims, Ms Rice said she was "surprised" and "shocked", calling it a "very serious allegation that has no basis in fact".
Devin Nunes, head of the House of Representatives intelligence committee, furthered Mr Trump's allegations last month after he said he viewed intelligence reports that included the names of Trump transition team officials.
But Adam Schiff, the top Democrat on the committee, said on Tuesday the White House "selectively and surreptitiously" gave Mr Nunes intelligence documents that should have been provided to the entire congressional panel.