South Korea's spy agency kept the highest North Korean official to have ever defected to Seoul from sending a memo to a senior North Korean official who visited Seoul more than a decade ago, a ruling party lawmaker said Wednesday.

Hwang Jang-yop tried to send a message to Jang Song-thaek, brother-in-law of then-North Korean leader Kim Jong-il, in 2002, when Jang visited South Korea, said Ha Tae-keung, a lawmaker of the ruling Saenuri Party, on a local radio broadcast.

Jang was a member of a North Korean delegation that made a rare trip to South Korea for an economic study tour following the landmark summit between the leaders of South and North Korea.

The North Korean delegation visited Samsung Electronics Co. and other South Korean industrial sites, business and transportation hubs, and research centers.

Hwang called on Jang to "make a determination," in the memo, noting it "is the last chance to serve the country and people," Ha said as he recalled his conversation with Hwang. It was not clear what Hwang meant by "determination."

But the National Intelligence Service, South Korea's top spy agency, prevented Hwang from sending the memo to Jang during his visit to South Korea.

Ha, who said he frequently met with Hwang since 2001, said the former North Korean official thought that Jang should assume power after Kim's death and pursue reform and openness in North Korea.

Hwang, who taught North Korea's "juche" philosophy of self-reliance to Kim, died in Seoul in 2010.

Kim died of a heart attack in 2011 and was succeeded by his youngest son, Kim Jong-un.

North Korea executed Jang in December 2013 on charges of treason. (Yonhap)