The White House has restricted access to transcripts of some of US President Donald Trump's calls with foreign leaders, US media report.
Officials said notes about calls to leaders including Russia's Vladimir Putin and the Saudi crown prince had not been handled in the usual way.
They say aides severely curtailed who saw them in a bid to stop leaks.
The White House has not so far commented on the claims, which follow the start of an impeachment inquiry.
Democrats launched the inquiry after the transcript of a 25 July phone call revealed that Mr Trump pushed Ukraine's President Volodymyr Zelensky to investigate discredited corruption allegations against Democratic presidential candidate Joe Biden and his son, Hunter.
Democrats accuse Mr Trump of illegally seeking foreign help in the hope of smearing Mr Biden - a frontrunner for the Democratic presidential nomination.
In a complaint filed last month, a whistleblower from the intelligence community reported his "urgent concern" that the president had used his office to "solicit interference from a foreign country" in the 2020 US election.
On Friday, the White House confirmed that the transcript had been placed in a separate system for highly classified information.
Mr Trump is also accused of using military aid for Ukraine as a bargaining tool. He has dismissed the proceedings as a "hoax" and "another witch-hunt". On Saturday he accused leading Democrats of "presidential harassment" and branded them "Democrat Savages".
On Friday, three House committees subpoenaed Secretary of State Mike Pompeo for documents about the administration's dealings with Ukraine.
Kurt Volker, US special envoy to the country, resigned on the same day.
What happened to the phone transcripts?
According to officials quoted in various US media outlets, the policy of restricting access to transcripts of some of the president's calls with foreign leaders began more than a year ago.
White House officials are said to have decided to act to prevent embarrassing leaks, such as when Mr Trump's conversation with then-Australian Prime Minister Malcolm Turnbull went public in 2017.
Even tighter restrictions came into place after his conversation with Russia's foreign minister appeared in the news.
This included limiting who was given a copy of the notes from the call, and also reportedly filing notes on certain calls away into classified information storage reserved for foreign surveillance and covert operations - rather than the usual system widely accessible to National Security Council officials.
For example, aides and officials who would normally see a rough transcript of the president's conversations reportedly never saw one for Mr Trump's call with Crown Prince Mohammed bin Salman and other Saudi royals.
The New York Times reports that the call came after the killing of Saudi journalist Jamal Khashoggi in October 2018. An official told the newspaper there was no evidence of improper behaviour by the president.
Access to a transcript of at least one conversation with Russian President Vladimir Putin was also curtailed.
It is unclear if notes on these calls were placed in the classified information storage system.