Insurgents launched a bold assault on the presidential palace compound in Afghanistan’s capital Tuesday morning, threatening to derail a critical stage in the country’s fragile peace process.

All the militants, who were disguised in foreign military uniforms and carried fake documents, were killed in the attack, the Taliban said in a statement, some when they detonated explosives and others in a gun battle with security forces. Three Afghan security guards also were killed, according to Interior Ministry spokesman Sediq Sediqqi.

The Taliban said the presidential palace, the Afghan Defense Ministry and a CIA outpost were the targets.

To both Afghan and Western officials, the attack casts cast doubt on the Islamist group’s willingness to engage in a constructive dialogue with the government of President Hamid Karzai and with U.S. officials. Karzai was already angered by the Taliban’s use of a plaque at its new office in Qatar’s capital that was labeled “Islamic Emirate of Afghanistan” and had canceled plans for Afghan negotiators to travel to the Persian Gulf nation for talks with U.S. and Taliban representatives on a political solution to the conflict.

With the Taliban diplomatic office on life support, many Afghans doubt whether the revival of peace talks would mean an end to attacks like Tuesday’s. Some argue that the Taliban would probably try to pursue a political settlement without ceasing high-profile attacks in Afghanistan — as the group signaled in a statement last week pledging not to “pose harm to other countries.”

Tuesday’s attack occurred less than a day after James Dobbins, the U.S. special representative to Afghanistan and Pakistan, visited Kabul for meetings with Afghan officials about the peace talks.

“All of the attackers were killed. . . . This again demonstrates the futility of the Taliban’s efforts to use violence and terror to achieve their aims,” U.S. Ambassador James B. Cunningham said in a statement. “We again call on the Taliban to come to the table to talk to the Afghanistan government about peace and reconciliation.”

Karzai said the attack showed that the Taliban militants “are against peace, stability and progress in Afghanistan,” the Associated Press reported.

The assault was one of several carried out by the Taliban in Kabul in recent weeks as part of its prolonged spring offensive. Many analysts contend that the group is attempting to prove its strength as the formal withdrawal of NATO combat troops nears.

Afghan forces, which last week took over responsibility for security throughout the country, have quelled many of those attempts, but the Taliban’s persistence points to a reserve of manpower and resources that the group says has not yet been tapped.

Gen. Abdul Zaher Cid of the Kabul police said that the insurgents wore uniforms that resembled those of the U.S.-led International Security Assistance Force and that the two armored vehicles used in the attack bore ISAF emblems.

One of the vehicles got past a security barrier using fake documents, while the second was stopped, deputy police chief Mohammed Daud Amin said.

The Taliban used a similar uniform-disguise tactic in a September attack on Camp Bastion in the southern province of Helmand in which a half-dozen U.S. Marine fighter jets were destroyed.