A suicide car bomber tore through the Afghan capital Saturday, just hours after President Hamid Karzai announced U.S. and Afghan negotiators had agreed on a draft deal allowing U.S. troops to remain in the country beyond a 2014 deadline.

The blast, which killed six people near where thousands of tribal leaders will discuss the deal this week, was a bloody reminder of the insecurity plaguing the country after 12 years of war.

The suicide bomber attacked security forces protecting the Loya Jirga site, Interior Ministry spokesman Sediq Sediqqi said. He said the blast killed six people and wounded 22. Among the dead were two security personnel, he said.

Sediqqi said Afghan security forces had prior knowledge of the suicide bombing, but were unable to stop the attack. He did not elaborate.

No group immediately claimed the attack, though blame is likely to fall on the Taliban, who have adamantly opposed the presence of any foreign soldiers in Afghanistan.

Karzai called for the Loya Jirga, a national consultative assembly of tribal elders, which will begin meeting Thursday to discuss the proposal. Some 3,000 elders and influential figures will debate the Bilateral Security Agreement.

Without its approval, Afghanistan likely will refuse to sign the agreement. If the Loya Jirga does approve it, the agreement still requires final approval from parliament, Karzai said.

U.S. officials refused to comment on the draft, describing the effort as an ongoing diplomatic process. Karzai provided few details regarding how and when the draft was finalized, but said there still remain “differences” between Washington and Kabul on the deal.