The United States and Afghanistan are close to clinching an agreement that will give Kabul more authority over night-time raids, resolving an issue that threatened to derail negotiations on a long-term U.S. military presence, U.S. officials said Tuesday.

"An agreement is days away," a U.S. official, who spoke on condition of anonymity, told Agence France Presse.

A U.S. delegation walked out of a regional conference in Tajikistan Monday after Iranian President Mahmoud Ahmadinejad lambasted U.S. policy on Afghanistan as the source of all the country's troubles.

Ahmadinejad launched his new tirade against Washington at a conference in the Tajik capital Dushanbe attended by leaders of Afghanistan's neighbors as well as a U.S. delegation led by Assistant Secretary of State Robert Blake.

Iranian President Mahmoud Ahmadinejad and his Pakistani counterpart Asif Ali Zardari arrived in Tajikistan on Saturday for regional security talks with Afghan leader Hamid Karzai.

The three are due to sit down with their Tajik host Emomali Rahmon on Sunday while a top US official is also due to meet diplomats from Pakistan and Afghanistan to discuss the outcome of Karzai's February visit to Islamabad.

The international community will subsidize Afghan security forces by more than $4 billion a year for a decade after U.S.-led combat forces leave Afghanistan in 2014, President Hamid Karzai said Thursday.

Western officials told Agence France Presse that no final agreement had been reached.

A U.S. soldier who allegedly shot and killed 16 civilians in Afghanistan was held at a U.S. military prison at Fort Leavenworth, Kansas, Saturday as new details emerged about the veteran's past.

The soldier, identified Friday as U.S. Army Staff Sergeant Robert Bales, had served three combat tours in Iraq, and was on his first deployment to Afghanistan.

The Taliban said Thursday it had suspended contacts with the United States in Qatar, just days after an American shooting spree left 16 Afghans dead, dealing a blow to hopes of a peace process.

"It was due to their alternating and ever-changing position that the Islamic Emirate was compelled to suspend all dialogue with the Americans," a statement posted on the Taliban website said, making no mention of Sunday's murders.

Afghanistan wants to take over control of the nation's security in 2013 not 2014 and for U.S. troops to pull out of villages, President Hamid Karzai said Thursday, just days after a U.S. soldier massacred 16 villagers.

Karzai told visiting U.S. defense chief Leon Panetta that "Afghanistan is ready to take overall security responsibility", a statement from his office said.

A roadside bomb attack killed eight civilians in Helmand on Wednesday as U.S. Defense Secretary Leon Panetta was visiting troops in a military camp in the southern Afghan province.

"A roadside mine planted by the Taliban blasted in Marja district when a minivan touched it, triggering a big explosion. As a result eight civilians were killed," provincial spokesman Daud Ahmedi told Agence France Presse.

The U.S. defense chief held talks in Afghanistan on Wednesday, acknowledging that a series of "deeply troubling" incidents had challenged the U.S. war effort but vowing that nothing would derail the mission to defeat al-Qaida and reverse a Taliban insurgency.

Leon Panetta held a series of meetings in southern Afghanistan just days after an American soldier went on a murderous rampage, shooting dead 16 Afghan civilians -- most of them women and children -- in the worst single such incident since the 2001 U.S.-led invasion.

The Afghan parliament demanded Monday that a U.S. soldier who went on a shooting spree and killed 16 villagers in their homes should be put on public trial in Afghanistan.

"We seriously demand and expect that the government of the United States punish the culprits and try them in a public trial before the people of Afghanistan," the lower house of parliament said in statement.