The Syrian government sent a complaint to the United Nations alleging that U.S. Sen. John McCain, R-Ariz., former French Foreign Minister Bernard Kouchner and former U.S. diplomat Peter Galbraith entered Syria illegally without visas to meet with rebel fighters.

In a letter sent to U.N. Secretary-General Ban Ki-moon and the 15-member Security Council, Syria's U.N. ambassador, Bashar Ja'afari, asked the council to pressure the responsible governments to take "the necessary measures against their nationals who enter Syrian territory illegally," reported Reuters.

"Such actions are a blatant violation of Syria's sovereignty and of the resolutions of the Security Council concerning Syria," Ja'afari wrote in the letter, complaining about "certain journalists and prominent figures" entering Syria illegally, but singling out McCain for his June 2013 visit.

McCain's spokesman said in summer 2013 that McCain visited Syria in May 2013 and met with some Syrian rebels, according to Reuters.

Media reports at the time said McCain crossed into Syria from Turkey with General Salem Idris, who was in charge of the Supreme Military Council of the Free Syrian Army.

In response, McCain said in a statement: "It is a sad but unsurprising truth that the Assad regime is less concerned with its massacre of more than 200,000 men, women and children than it is my visit with those brave Syrians fighting for their freedom and dignity.

"The fact that the international community has done virtually nothing to bring down this terrible regime despite its atrocities is a stain on our collective moral conscience."

McCain made another controversial visit to Kiev, Ukraine in December 2013, where he met with a Ukrainian opposition leader accused of being an anti-Semitic Neo-Nazi, and voiced support for the protests, reported Business Insider.

In 2011, McCain visited Benghazi to meet with Libyan rebels who he referred to as his "heroes," reported CBS News.

Ja'afari also said Kouchner visited in November 2014 and Galbraith in December 2014, along with other U.S. political and military leaders.