Afghan officials say gunmen assassinated a top Afghan peace negotiator Sunday, dealing a major blow to efforts aimed at ending the decade-long war.

Authorities say Arsala Rahmani, a senior member of the 70-member High Peace Council, was on his way to work when he was shot dead from a nearby car while stuck in heavy traffic.

Rahmani had served as a deputy education minister during the Taliban's rule in Afghanistan. He recently reconciled with the government and was actively trying to promote contacts with the militants.

The Taliban has denied responsibility for the attack.

The head of the council, former President Burhanuddin Rabbani, was assassinated last year by a suicide bomber.

Afghan President Hamid Karzai, Pakistan, the United States and NATO-led international forces have condemned Rahmani's killing.

Mr. Karzai called Rahmani's death a terrible loss. He said “enemies of the Afghan people once again proved that they fear peace in Afghanistan and resort to targeting those who seek dignity and prosperity for Afghanistan and are working to ensure peace and welfare in their country.”

Pakistan said it is committed to working closely with Afghanistan to eliminate terrorism.

The U.S. Embassy in Kabul said in statement Sunday, the “High Peace Council has been working for a durable, long-term peace in Afghanistan,” and that the U.S. will “continue to stand alongside the Afghan government and people against terrorism and to work with them on behalf of a secure and prosperous Afghanistan.”

NATO offered condolences and prayers to Rahmani's family and friends and said the “only possible aim of this attack is to intimidate those, who like Rahmani, want to help make Afghanistan a better place for its citizens and the region.”

In other violence, NATO said two of its service members were killed in a bomb blast in eastern Afghanistan.

Meanwhile, Afghan officials say they are taking the lead from the international coalition for providing security in areas that make up 75 percent of the country's population.

The Afghan government announced Sunday that it was launching the third phase of the transition of military control.

The first two phases already have put Afghans in control of areas representing half of the country's population. The final stage is set to be completed by the end of 2014, when most foreign combat troops are scheduled to leave.