President Donald Trump is facing new scrutiny over his calls with world leaders after a whistleblower flagged a July 25 call with the Ukrainian president, in which Trump urged him to investigate a political rival.

The whistleblower alleged that a number of presidential transcripts have been locked away in a codeword-level system "solely for the purpose of protecting politically sensitive — rather than national security sensitive — information."

White House advisers such as former chief of staff John Kelly even sought to prevent Trump from divulging sensitive information to world leaders, The Wall Street Journal reported Saturday.

Kelly reportedly used to mute the line and urge Trump to stop discussing sensitive information.

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The former White House chief of staff, John Kelly, used to mute the line during President Donald Trump's calls with world leaders to tell him not to continue discussing sensitive information, The Wall Street Journal reported Saturday, citing a person with knowledge of the matter.

The news comes amid political turmoil over a recent call in which Trump urged the Ukrainian president to investigate former Vice President Joe Biden, one of Trump's main political rivals.

The July 25 call with President Volodymyr Zelensky was the subject of an explosive whistleblower complaint and has spurred an impeachment inquiry from House Democrats.

Read more: The White House reportedly tried to conceal transcripts of Trump's calls with other world leaders, including Russia's Putin and Saudi Arabia's Mohammad bin Salman

The controversy has cast new scrutiny over Trump's previous communications with other world leaders. The whistleblower indicated in his complaint that a number of presidential transcripts have been locked away in a codeword-level system "solely for the purpose of protecting politically sensitive — rather than national security sensitive — information."

The Journal reported Saturday that White House advisers such as Kelly sought to prevent Trump from divulging sensitive information to world leaders on such calls, and other government officials sought to keep a tight lid on records of those conversations.

John Kelly. Alex Wong/Getty Images

Their efforts began after a number of controversies at the onset of Trump's presidency, including an infamous call with then-Australian Prime Minister Malcolm Turnbull, in which Trump lambasted a "rotten" refugee deal the Obama administration brokered with the Australian government.

Trump also took heat for another contentious phone call with then-Mexican President Enrique Peña Nieto, reportedly telling him, "We are going to build the wall and you all are going to pay for it, like it or not."

Read more: Trump's actions with Ukraine were 'profoundly stupid' and beyond anything any president has ever done, historians and veteran diplomats say

After the Australia and Mexico calls, the National Security Council "severely cut back" on the number of people to whom those call records were sent, The Journal reported, citing people knowledgeable of the situation.

Instead, the call records were sent only to people directly involved in the issues discussed in the call, according to The Journal's sources.