A vocal North Korean defector activist has left for the United States for a congressional hearing on a controversial bill South Korea recently passed to ban the sending of anti-North Korea leaflets, his lawyer said Thursday.

Park Sang-hak, a North Korean defector who runs Fighters for a Free North Korea, flew to Washington on Wednesday to attend the hearing that Rep. Chris Smith (R-NJ) is seeking to convene to discuss the anti-leafleting law.

"Park left for the US yesterday for the purpose of attending the US Congress hearing and other reasons with a plan to return in early March," said Lee Heon, a lawyer serving as Park's legal representative.

When the hearing will take place has yet to be determined, he added.

In December, the National Assembly, controlled by the ruling Democratic Party, passed the bill penalizing the sending of anti-Pyongyang propaganda leaflets into the North despite strong objection by opposition party lawmakers.

The ban came after North Korea bristled at such activity and even blew up an inter-Korean liaison office in June last year. Pyongyang has denounced the leafleting as a violation of inter-Korean agreements and demanded that Seoul take preventive measures.

Critics have claimed that such a ban is tantamount to caving to Pyongyang's pressure. US politicians and others have also said that the legislation could erode freedom of expression and block one crucial avenue for sending free world information into the reclusive country.

Park, a defector-turned-activist, earlier filed a constitutional complaint against the ban. (Yonhap)