Afghan President Hamid Karzai has ruled out further talks with the Taliban, saying “we cannot keep talking to suicide bombers.”

After a summit meeting Tuesday with his Pakistani counterpart, Asif Ali Zardari, and Turkish President Abdullah Gul, in the Turkish city of Istanbul, Mr. Karzai said his government would instead continue to talk with Pakistan about finding solutions to the insurgency-related violence.

Mr. Gul, who hosted the summit, said Pakistan agreed to cooperate with Afghanistan on a joint inquiry into the September 20 assassination of Afghanistan's top peace negotiator, former President Burhanuddin Rabbani. He said the two sides established a cooperation mechanism and the investigation will be coordinated by the two countries' foreign ministries and will involve their intelligence services.

Afghan officials accused Pakistan's military spy agency of involvement in the attack, a charge Pakistan strongly denies.

Rabbani, who was seeking to negotiate with the Taliban to end their insurgency, was killed by a suicide bomber. His killing has worsened already difficult relations between the two South Asian neighbors.

In an effort to reduce tensions, Afghan and Pakistan military leaders also held talks in Istanbul Tuesday, along with their Turkish counterparts.

The meeting between the presidents of Afghanistan and Pakistan was the first since Rabbani's death and came a day before foreign ministers from 14 countries participate in a regional summit on development and aid, again hosted by Turkey.

The gathering will focus on Afghan efforts for a political solution to the decade-long conflict and security and economic development in Afghanistan as foreign combat troops reduce their presence in the country and leave by the end of 2014.

Observers say creating a positive political momentum in relations between the two countries is important ahead of international meetings on Afghanistan set to take place in Bonn, Germany in December, and in the U.S. city of Chicago next year.