Two U.S. senators have been barred from visiting the Philippines over a measure that seeks to punish Philippine officials involved in the detainment of a top critic of President Rodrigo Duterte's anti-drug crackdown.

Salvador Panelo, a spokesman for Duterte, said during a news conference Friday that the Philippine president ordered the Bureau of Immigration to deny Senators Dick Durbin, a Democrat from Illinois, and Patrick Leahy, a Democrat from Vermont, entry into the country.

"We will not sit idly if they continue to interfere with our process as a sovereign state," Panelo said during a news conference.

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The provision protested by the Philippine government was included in the spending package passed by Congress last week. It denies entry to the U.S. to those involved in the incarceration of Philippine Senator Leila de Lima, according to Reuters.

De Lima, an ardent critic of Duterte's anti-drug campaign, was arrested in 2017 and led an investigation into mass killings that took place during the Philippine president's drug war.

David Carle, a spokesman for Leahy, said the senator has no plans to visit the Philippines in the near future and is not aware at this time of any Philippine officials planning to visit the U.S. who may be subject to the new restrictions.

"This is about the right of Filipino citizens — and people everywhere — to freely express their opinions, including opinions that may be critical of government policies that involve the use of excessive force and the denial of due process," Carle said.

In addition to prohibiting Durbin and Leahy from entering the Philippines, the Philippines will require American citizens to secure a visa before entering the country if the restrictions are enforced by the U.S. against Philippine officials.

U.S. citizens can enter the Philippines without a visa for visits under 30 days, according to the State Department.