North Korea's vice premier Choe Yong-Gon has been executed for voicing frustration at the policies of leader Kim Jong-Un, South Korea's Yonhap news agency says.

Mr Choe, who took the job in June 2014, was executed by firing squad in May after voicing opposition to forestry policies promoted by Mr Kim, Yonhap said, citing an anonymous source "with knowledge of the North".

The vice premier has not been mentioned in the North's state media since last October, it added, in another apparent sign he had been purged.

The execution of the 63-year-old former delegate for North-South cooperation marks another death of a senior official in a series of high-level purges since Kim Jong-Un took charge in late 2011.

Mr Choe's death, if confirmed, would be the second reported this year.

Defence minister Hyon Yong-Chol was said to have been executed in April by anti-aircraft fire for insubordination and dozing off during formal military rallies.

South Korea's Unification Ministry, which handles the country's ties with North Korea, said Mr Choe had not been spotted in public for about eight months and that it was closely monitoring the situation.

Mr Choe had worked on inter-Korean affairs in the 2000s, leading the North's delegation in joint economic cooperation committees with South Korea between 2003 and 2005.

He attended the 2004 opening ceremony of the Kaesong Industrial Complex, a factory park run by the North with Seoul that is the last remaining joint project of the two countries.

AFP/Reuters