U.S Secretary of State John Kerry said on Thursday he had "zero communication" with anyone in the U.S. administration on a Pacific trade pact in connection with Malaysias upgraded designation on human trafficking.

The State Department late last month took Malaysia off its list of worst offenders in human trafficking, removing a potential barrier to a signature Asia-Pacific trade pact, despite opposition from human rights groups and nearly 180 U.S. lawmakers.

"Let me just be crystal clear, because I am the person who approved this, I personally signed off on it, I had zero conversation with anyone in the administration about the Trans Pacific partnership relative to this decision," Kerry said in the Malaysian capital, where he has been attending a regional conference.

On Tuesday, senior U.S. lawmakers expressed concern about whether the State Departments annual global report on human trafficking may have been watered down due to political considerations and vowed to demand a full accounting at a Senate hearing this week.

Human rights groups also called for an investigation into why strategically important countries such as Malaysia were upgraded in the report, after a Reuters article chronicled how senior U.S. diplomats repeatedly overruled State Department human rights experts.

"Obviously the Congress has a right … they have every right in the world to take a look to see whether or not its being implemented in the way Congress intended. I am absolutely confident in the work that our TIP (Trafficking in Persons) team does, which literally takes an entire year to do," Kerry said.

Kerry met Malaysian Prime Minister Najib Razak on Wednesday and noted steps his government has taken to address human trafficking but urged it to ‎improve law enforcement and victim protection, a U.S. State Department official said.

A Reuters examination based on interviews with more than a dozen sources in Washington and foreign capitals, showed that the State Department office set up to independently grade global efforts to fight human trafficking was pressured into inflating assessments of 14 countries in this year’s report.

Among the countries that received higher rankings than recommended by the Office to Monitor and Combat Trafficking in Persons were Malaysia, Cuba, China, India, Uzbekistan and Mexico, the sources said.