MANILA (UPDATE) — President Rodrigo Duterte has formalized his order banning Cabinet secretaries from attending a Senate investigation into the alleged misuse of pandemic funds.

Duterte on Monday night said he has issued a memorandum prohibiting his aides from joining the probe "because we cannot allow blatant disrespect of resource persons at the ongoing hearings of the Senate Blue Ribbon Committee."

Addressing Sen. Richard Gordon, chair of the committee, Duterte said, "You are not God and you cannot play God. No. You cannot continue this hearing 'til Kingdom come."

"You are not a senator forever and the time of reckoning will come. You and the Senate cannot compromise the government's COVID-19 response by getting agency leaders tied up for so long at your beck and call," he said in a taped late night speech.

Malacañang later confirmed the issuance of the memorandum.

"This latest Presidential directive is based on the premise that the principle of separation of powers requires mutual respect among the different branches of government, and in view of Article II, Section 15 of the 1987 Constitution on the protection and promotion by the State of the right to health of the people," presidential spokesperson Harry Roque said in a statement.

The Senate in its hearing on Tuesday showed portions from the memo signed by Executive Secretary Salvador Medialdea.

"On the premise that the principle of separation of powers requires mutual respect among the different branches of government… the President has DIRECTED all officials and employees of the Executive Department to no longer appear before or attend the above mentioned Senate Blue Ribbon Committee hearings, effective immediately," it reads.

"Instead, they shall focus all their time and effort on the implementation of measures to address the current State of Calamity on account of COVID-19, and carrying out their other functions," added the memo.

Health Secretary Francisco Duque III and other officials were absent in Tuesday's hearing. Only customs, internal revenue, and civil service executives attended.

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The officials' absence runs counter to Roque's remark on Monday that they would continue cooperating with the probe as they had nothing to hide.

A group of 13 high-profile academic, business and religious organizations has urged government cooperation in the probe "to the fullest extent allowed by law."

"We call on lawmakers, members of the executive department, constitutional commissions and, if they are brought in, members of the judiciary to conduct their proceedings with integrity, transparency, and respect, and in compliance with our laws and established procedures," the statement added.

The investigation follows the state auditor's flagging of P67-billion "deficiencies" in how supply contracts were handled. The funds were allocated to cover benefits of health workers and medical supplies.

Duterte last month ordered Cabinet members to seek his consent before appearing in Senate hearings. His government has denied misuse of the funds.

"There is no iota of evidence of overpricing or money lost to corruption," Duterte said in a late night address Monday, and told senators not to use the investigation "as a witch hunt in aid of election."

He said he was not opposed to the Senate investigation but disapproved of how the public inquiries, which last for hours, have interfered with the work of cabinet members required to attend, including those related to the pandemic response.

The Philippines has recorded more than 2.6 million COVID-19 cases and over 38,800 deaths, and is one of Asia’s worst-affected countries in terms of casualties and economic losses.

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The group's call for a transparent investigation comes at a sensitive time for the Duterte administration, just days away from the closing of a window for many of his allies to file candidacies for elections next year.

Duterte, 76, who was elected on promises to eliminate graft completely, cannot seek a second term and had been expected to run for vice president next year.

But over the weekend he declared he would retire from politics, days after an opinion poll on preferred vice president candidates showed him slipping into second place. He had done the same in 2015, claiming he would leave politics for good but surprised many when he became a presidential candidate via substitution.

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— With reports from Sherrie Ann Torres, ABS-CBN News; and Reuters