The Pentagon on Monday expressed optimism on the prospects of an eventual security agreement between the United States and Afghanistan, despite a vow by Kabul to suspend the talks.

President Hamid Karzai called off the negotiations on a future US military presence in Afghanistan after 2014, saying the discussions would only resume when Taliban insurgents meet with Afghan government representatives for possible peace talks.

"We do hope to make progress in the near future on the Bilateral Security Agreement," Pentagon spokesman George Little told reporters.

He said discussions would continue and that "the bilateral security agreement process is moving forward."

The United States and NATO allies, Arab countries and Pakistan have pushed both Karzai and Taliban leaders to start a dialogue that might lead to peace negotiations.

But when the Taliban opened an office in the Qatari capital Doha that diplomats had seen as a venue for talks, the insurgency portrayed the office as an embassy for an alternative government for Afghanistan, prompting outrage in Kabul.

The Taliban has consistently refused to hold any talks with the Afghan government, with the hardline Islamists labeling Karzai as a puppet of the United States.

With the bulk of US and NATO combat forces due to withdraw in 2014, the security agreement would set the number of troops allowed in the country, specify which bases the US forces would be permitted to use and provide legal immunity to the American forces.