A leading senator has charged that Hillary Clinton’s State Department broke the law by intentionally obfuscating and downplaying to Congress the terror threat posed by the Nigerian extremist group Boko Haram, which recently gained international infamy for violently kidnapping more than 200 schoolgirls.

Sen. David Vitter (R., La.), a member of the Senate Armed Services Committee, petitioned Secretary of State John Kerry on Monday to explain why Clinton’s State Department misrepresented and downplayed key information about Boko Haram’s terrorist activities in its annual reports to Congress.

Former Secretary of State Clinton lied to Congress when she said that the State Department lacked the necessary information to designate Boko Haram as a terror group, according to Vitter’s letter, which presents new information about the State Department’s purported efforts to downplay the terror group’s impact.

Clinton’s State Department fought against efforts to designate Boko Haram for nearly two years, a move that likely limited U.S. efforts to confront the group earlier and allowed it to grow in strength.

Vitter charges that officials working under Clinton intentionally manipulated words and mislead Congress in its annual reports to create the impression that Boko Haram posed little to no threat.

Clinton’s State Department "repeatedly stated in the year leading up to the designation that it did not have data available or the necessary understanding to make the determination," Vitter wrote to Kerry, according to a copy of unreleased letter obtained by the Washington Free Beacon.

However, "recent evidence suggests Secretary Hillary Clinton and the State Departments not only knew of the extent, but also deliberately attempted to obfuscate the issue in order to avoid having to make the designation of Boko Haram as a [Foreign Terrorist Organization], including downplaying the State Department’s own Country Reports on Terrorism (CRT)," Vitter writes.

"Inaccuracies within official documents make it clear that the State Department misled Congress and the American people," the letter states. "Evidence suggests that there was an internal decision by the Office of Coordinator for Counterterrorism to downplay official, legally required, intelligence data in order to purposefully avoid making the determination."

Vitter demands in a series of questions that Kerry provide answers as to why the State Department "ignored data and misrepresented its legal requirements to Congress."

U.S. law stipulates that the State Department provides Congress with "statistical information supported by data" in its annual reports on terrorist activities in foreign countries.

Officials in Clinton’s State Department failed to uphold this mandate, Vitter charges, citing evidence that reports of Boko Haram’s activity by the National Counterterrorism Center (NCTC) were intentionally ignored.

The NCTC in 2011 "provided the State Department with the statistical information necessary to determine that Boko Haram was engaged in terrorist activity," Vitter writes. "However, in completing the official annual CRT provided to Congress" at that time "the State Department chose not to include this information."

New evidence suggests that NCTC information about Boko Haram’s terrorist activities was intentionally left out of the State Department’s reports to Congress, a move that effectively left lawmakers in the dark about the extremist group’s growing influence.

"In multiple cases, where the NCTC clearly labeled and claimed that Boko Haram was engaged in terrorist activity against foreign nations, Secretary Clinton’s office in their own report minimized the attack and separated the issue from Boko Haram," according to Vitter’s letter.

A 2012 NCTC report, for instance, stated that Africa experienced 978 attacks in 2011, representing an 11.5 percent increase from 2010 levels.

This uptick was attributed "in large part to the more aggressive attack tempo of the Nigeria-based terrorist group Boko Haram," according to a portion of the NCTC report included in Vitter’s letter.

The NCTC further reported in that year that Boko Haram had conducted a terror attack against Western targets, accounting for "the largest terrorist attack in the country to date," according to the report.

Yet Clinton’s State Department deemphasized this data and "only chose to include loose evidence" in its own terrorism report to Congress, Vitter states.

"The conflict in Nigeria continued throughout the northern part of the country with hundreds of casualties as indigenous terrorist attacks increased," the State Department wrote in its report to Congress at the time. "The Nigerian extremist group, Boko Haram, claimed responsibility for some of these attacks."

Vitter says that this phrasing is proof of the State Department’s bid to create the impression that Boko Haram was a minimal threat.

"It appears that this variation in wording fails to meet the legal requirements based on information it received, and inserts a higher degree of doubt about whether Boko Haram is directly engaged in terrorist activity," Vitter writes.

The State Department report issued under Clinton "ignores the NCTC labeling Boko Haram as a ‘terrorist group,’ instead suggesting that there may be a loose connection," Vitter further adds.

"These facts are troubling considering multiple official reports between 2010 and 2012, including the Global Terrorism Database, concluded that Boko Haram was improving their capability to coordinate on an operational level with al Qaeda affiliates, including al Qaeda in the Islamic Maghreb (AQIM) and al-Shabaab."

Boko Haram has a long history of terrorism, having detonated a car bomb at a United Nations headquarters in Abuja, an attack that killed 23 and injured 81 others.

The State Department’s own reports from 2009 to 2013 further demonstrate that Boko Haram "steadily increased in deadliness and its connectivity to terrorist organizations," according to Vitter’s letter.

Boko Haram has even gone on to top al-Shabaab and al Qaeda in the Arabian Peninsula as the leading regional terrorist group, having killed nearly 4,000 people from 2009 to 2013.

Independent terrorism analysts have determined that Boko Haram and al Qaeda have been linked for more than a decade, and that the extremist group has ties to a least six al Qaeda affiliates, according to a recent report by the Henry Jackson Society (HJS).

There is also evidence that Boko Haram has taken direct orders from al Qaeda, according to HJS.

Yet the annual report to Congress "goes out of its way to downplay the effectiveness or lethality of the group." Boko Haram’s connections to al Qeada were clear to U.S. authorities from at least 2010 on, according to information from the NCTC.

Following Boko Haram’s successful and deadly attack on the U.N.—an incident the NCTC dubbed "the largest terrorist attack in the country to date—Clinton’s State Department "largely dismissed the events and that data, claiming" in its report to Congress that "no terrorist attacks occurred in the Southern states of Nigeria."

Independent terrorism analyst Olivier Guitta, research director for HJS, warned in a recent statement that "the international community has been underestimating Boko Haram, even though it is in the top 3 of the bloodiest terrorist groups in the world."

Vitter is seeking answers as to why the State Department "manipulated words" and misled Congress.

"The State Department’s documents may have failed to explicitly label Boko Haram as a terrorist organization, in almost complete disregard of specific [National Counterterrorism Center] data, but my concern goes deeper to address the internal decision to manipulate words and mislead Congress," he states in the letter to Kerry.

"The evidence suggests that the office of the Coordinator for Counterterrorism may have intentionally exploited the statistical information provided to them by law in an attempt to neglect Boko Haram’s terrorist activity," he adds.

Vitter has given Kerry until July 10 to respond to his queries about the issue.