MANILA, June 20 (Reuters) - Lawmakers in the

Philippines, including the head of the Senate's foreign

relations committee, are seeking an investigation into a secret

U.S. military propaganda operation that aimed to cast doubt

among Filipinos about China's vaccines during the height of the

COVID pandemic.

Philippine Senator Imee Marcos, who chairs the foreign

relations committee, and House Representative France Castro

filed resolutions in the country's Congress this week to

initiate the probe, according to documents reviewed by Reuters.

A Reuters investigation last week detailed how the Pentagon

ran a clandestine influence campaign in 2020 and 2021 to

denigrate the Sinovac vaccine and other pandemic aid from China

across the developing world. The effort was intended to counter

what Washington then saw as China's growing geopolitical sway

around the globe, including in Southeast Asia. It began under

former President Donald Trump and ended months after President

Joseph Biden took office.

The Senate inquiry is intended to examine the Reuters

findings and "determine the ramifications of the actions of the

U.S. Military, any potential breach of international law by the

United States of America, and the possible legal recourse

available to the Philippines, considering that such (an)

anti-vax and misinformation campaign threatens national

security," according to the resolution from Marcos, sister of

Philippine President Ferdinand Marcos Jr.

Castro's resolution, which was also signed by two other

lawmakers, urges the nation's House of Representatives to

conduct an investigation into the U.S. military campaign. It

says "such underhanded tactics by a foreign military power

sowing disinformation in the Philippines are a brazen affront to

our national sovereignty and the democratic rights of Filipinos

to freely access truthful information vital to public health and

safety."

A senior Defense Department official acknowledged to Reuters

that the U.S. military engaged in secret propaganda to disparage

China's vaccines in the developing world during the pandemic,

but declined to provide details. The official said that new

policies and controls had been put in place, following an

internal review in 2021, that would block similar operations in

the future.

A Pentagon spokeswoman said that the U.S. military "uses a

variety of platforms, including social media, to counter those

malign influence attacks aimed at the U.S., allies, and

partners." She also noted that China had started a

"disinformation campaign to falsely blame the United States for

the spread of COVID-19."

Senator Marcos told reporters in the Philippines this week

that she was motivated to investigate the matter because she

believed it may have put the lives of Filipinos at risk. At the

time of the secret U.S. military operation, the primary vaccine

option in the Philippines was China's Sinovac inoculation.

During the pandemic, the Philippines suffered among the worst

COVID infection rates in the region, and officials struggled to

persuade its citizens to get vaccinated.

The Reuters investigation was based on interviews with more

than two dozen current and former U.S officials, military

contractors, social media analysts and academic researchers.

Reporters also reviewed Facebook, X and Instagram posts,

technical data and documents about a set of fake social media

accounts used by the U.S. military.

Reuters could not determine what impact the military's

influence campaign had on public health in the Philippines. But

some American public health experts say the propaganda program

endangered lives. "I don't think it's defensible," said Daniel

Lucey, an infectious disease specialist at Dartmouth's Geisel

School of Medicine. "I'm extremely dismayed, disappointed and

disillusioned to hear that the U.S. government would do that."

In a statement to Chinese media, a Sinovac spokeswoman also

decried the U.S. military's campaign. "Stigmatizing vaccination

will lead to a series of consequences, such as a lower

inoculation rate, the outbreak and spread of disease, social

panic and insecurity, as well as crises of confidence in science

and public health," said Sinovac spokeswoman Yuan Youwei.