Afghan President Hamid Karzai is preparing to meet Nato leaders in Lisbon for talks on withdrawing troops from his country by the end of 2014.
A spokesman for Mr Karzai said he and Nato shared the "same strategic interests" but that there were many issues still to be worked out.
Russian President Dmitry Medvedev is also due to address the summit.
On Friday, the military alliance agreed to develop a joint missile defence shield covering all member states.
The Portugal summit also backed the swift ratification of the Start treaty between the US and Russia, aimed at cutting the nuclear weapon stockpiles of both sides.
Nato's International Security Assistance Force (Isaf) has some 130,000 soldiers based in Afghanistan, most of them from the US.
US President Barack Obama said the Isaf mission was "moving to a new phase", and that the target for handing over the overall responsibility for security to the Afghans was still 2014.
Some Nato members have expressed concerns that Afghanistan may not be ready to manage its own security by that time, but Secretary General Anders Fogh Rasmussen has said the goal is "realistic".
Mr Rasmussen said there would still be a role for Isaf troops in the country in 2015 and onwards, but that would largely be in training Afghan forces.
BBC News
