Following a trilateral summit, the leaders also pledged to step up cooperation for eradicating terrorism and militancy and said they would not allow "any threat emanating from their respective territories against each other".
A joint statement issued after the summit said the three Presidents had agreed to "proceed on the basis of mutual interest, mutual respect, non-interference and non-intervention in internal affairs".
Official sources told PTI that US-led efforts to hold negotiations with the Afghan Taliban and sanctions imposed by Western powers in connection with Iran`s nuclear programme had figured in both bilateral discussions between the Presidents and the trilateral summit.
The statement said the three countries "reiterated their full support for an Afghan-led and Afghan-owned inclusive process of peace and reconciliation" in Afghanistan.
Pakistan President Zardari and Iranian President Mahmoud Ahmadinejad assured Afghan President Hamid Karzai that they would "extend full cooperation and stressed that any initiative in this regard must have authentic Afghan ownership", the statement said.
Though the statement made no mention of the sanctions imposed on Tehran or reported Israeli threats to mount an attack on Iran, the statement said the three countries would not "allow any threat emanating from their respective territories against each other". They also agreed to "commence trilateral consultations on an agreement in this regard", the statement said without giving details.
TV news channels quoted their sources as saying that Zardari had assured Ahmadinejad that Pakistan would not allow the US or any other country to use its soil to mount an attack on Iran. There was no official word on the reports.
During a joint news conference with Ahmadinejad and Karzai, Zardari said Pakistan was determined to forge ahead with projects with Iran, like a multi-billion dollar gas pipeline, and that relations between Islamabad and Tehran cannot be "undermined by any international pressure of any kind".
Ahmadinejad contended that problems were being foisted on the countries of the region by external powers. He did not identify these powers. "We should stand together to advance and realise our goals... We believe that problems of the region must be solved regionally," Ahmadinejad added.
Zardari denied that Pakistan`s armed forces were involved in backing militant groups in Afghanistan but acknowledged that elements linked to the jihad against the erstwhile Soviet Union could still be working with the rebels.
The joint statement said the three Presidents pledged to enhance cooperation "for realising the shared aspiration of their peoples for peace, security, stability and economic prosperity". They agreed to develop a framework for comprehensive cooperation and to take "pragmatic steps for realising mutually beneficial cooperation to promote stability, peace and shared prosperity". They further pledged to ensure "respect for sovereignty, independence, unity and territorial integrity as enshrined in the UN Charter".
Besides agreeing on contributing to development and reconstruction in Afghanistan, the three leaders decided to cooperate in combating narcotic drugs production and trafficking and transnational organised crimes. They also agreed to enhance three-way trade by facilitation measures, including preferential tariffs, free trade arrangements and barter trade. They further agreed to enhance connectivity by promoting project cooperation in infrastructure, road and rail links, transport and communications and to develop mutually beneficial cooperation in the energy, mining and agriculture sectors.
The Presidents directed their Foreign Ministers to prepare and coordinate a roadmap for trilateral cooperation for submission to the next Summit to be held in Kabul. They also directed the Interior Ministers to develop a framework of cooperation, particularly in counter-terrorism, counter-narcotics and border management within six months.
This was the third trilateral summit of Afghanistan, Iran and Pakistan. The three Presidents had met in June last year. The next meeting will be held in Kabul by the end of the year.