Afghan President Hamid Karzai attends an event to commemorate Afghanistan's 95th anniversary of independence in Kabul August 19, 2014. [Photo/Agencies]

KABUL - President Hamid Karzai will not attend a key NATO summit next week because of his disagreements with Washington over Afghan security needs after most foreign troops leave his country at the end of 2014, his spokesman said on Tuesday.

The Sept 4-5 summit in Wales is meant to determine how much aid Afghan security forces will get after NATO's combat mission ends. The alliance wants a smaller force to stay beyond 2014 to train and advise the security forces but it needs the Kabul government's consent -- something Karzai has refused to give.

Karzai has refused to sign a bilateral security deal with the United States allowing its troops to stay beyond this year, demanding certain conditions be met first.

Those conditions include ending military operations on Afghan homes, taking steps towards making peace with the Taliban and returning Afghan inmates held at Guantanamo prison camp.

Karzai's refusal to ink the deal has fueled anxiety among Afghans about the future, as a similar pact with NATO countries also remains unsigned as a result, raising the prospect of a full pull-out of international troops by the end of this year.

Afghanistan's 350,000-strong security force currently costs about $6 billion to run and is mostly funded by foreign donors. If international forces leave altogether, much of the money pledged by the donors could also follow.

The candidates to succeed Karzai after June's presidential election have both said they would sign the agreements, but they are locked in a dispute over the poll results and it could take weeks before a new president is installed.

Officials in Kabul have suggested the most likely person to attend the NATO summit is the defence minister, but the government has not confirmed this.