Direct correspondence between Indonesian President Susilo Bambang Yudhoyono and Singapore Prime Minister Lee Hsien Loong has failed to resolve key issues holding up the Defence Cooperation Agreement (DCA).

The leaders of both countries stepped in after negotiations in May reached an impasse, Indonesian Defence Minister Juwono Sudarsono disclosed this in an interview with The Straits Times.

In addition, Dr Juwono had also been exchanging letters with his Singaporean counterpart Teo Chee Hean, with military chiefs on both sides doing the same.

Still, both President Yudhoyono and PM Lee agreed to continue with a fresh talks to smooth over differences over implementing arrangements (IAs) related to the DCA, but they stopped short of committing to a specific time frame.

The IAs provide details on the conduct of military exercises to be carried out under the DCA.

The original arrangement was for the DCA, IAs and an extradition treaty to be concluded as a package on April 27 in Bali. However, at Indonesia's request, the signing was supposed to be delayed to May 7. That also failed to materialise after Indonesia requested significant changes.

Indonesian politicians have been critical about allowing foreign troops on Indonesian soil, and felt that this would undermine national sovereignty. Dr Juwono himself had previously hit out at Singapore for rejecting Indonesia's request to jointly draw up details for the use of the training zone and asking for military exercises to be held there for 15 days a month.

According to the Ministry of Foreign Affairs, Singapore's position is that because the pacts are already settled, the terms cannot be changed without jeopardising the whole package.

MPs will hear more details of the negotiations with Indonesia in Parliament today.