US Secretary of State John Kerry will meet on Wednesday with Afghan President Hamid Karzai, the head of Pakistan's armed forces and Pakistan's foreign minister.

In Brussels for a gathering of NATO foreign ministers on Tuesday, Kerry said: "I'll be meeting with President Karzai and with General Kayani and with the civilian foreign minister (Jalil Abbas Jilani) from Pakistan while I'm here."

Kerry said on Monday the aim was to "try to talk about how we can advance this process in the simplest, most cooperative, most cogent way so that we wind up with both Pakistan's and Afghanistan's interests being satisfied, but most importantly, with a stable and peaceful Afghanistan."

A US diplomatic source said earlier that Afghan Defence Minister Bishmullah Mohammadi would also attend.

The meeting, which was not originally on Kerry's agenda, is part of a series between the three parties, the source said, with neighbouring Pakistan a key player as NATO forces prepare to withdraw from Afghanistan in 2014.

Afghanistan is high on the agenda for Tuesday's NATO meeting, alongside the conflict in Syria and the transition to a UN peacekeeping force in Mali, for Kerry's first trip to the alliance headquarters as US secretary of state, as NATO prepares to hand over security duties to the Afghan national army.

Relations between Islamabad and Kabul have been strained for many years, with Karzai charging Pakistan with aiding and abetting the Taliban rebels who seek refuge along their rugged border.