North Korean leader Kim Jong Il repeatedly pushed for summit talks before his death in 2011 - but demanded £6.6 billion and huge shipments of food and fertiliser in return, South Korea's former president has said.

The revelation emerged in an autobiography by Lee Myung-bak due to be published next week.

The book says senior officials from the two Koreas made secret visits to the rival countries to explore summit possibilities in 2010, when two deadly attacks blamed on Pyongyang killed 50 South Koreans.

Mr Lee said a Pyongyang envoy who came south was later publicly executed after returning to the North.

The Koreas have held two summit talks in 2000 and 2007 since their division 70 years ago.

Mr Lee's book comes as both countries float the idea of a possible summit between Kim's son and current leader, Kim Jong Un, and Mr Lee's successor, President Park Geun-hye. It would be the third such meeting since the two Koreas were divided 70 years ago, although chances seem low as the countries bicker over the terms for a meeting.

The first summit in 2000 prompted an era of co-operation between the rivals, but it also became a source of criticism in South Korea. Conservatives said Seoul's then "sunshine policy" of providing generous economic aid to Pyongyang with few strings attached propped up the North's nuclear and missile development.