"There are countries that are determined to dominate our region. And they have targeted our region for their domination and hegemony," he told a news conference in Islamabad.
"We should deny others the opportunity to interfere in our affairs."
The Iranian president did not say to which countries he was referring.
The West accuses Iran of using its nuclear programme to pursue weapons capability and has imposed sanctions on its oil industry which have hit its wider economy hard.
Iran rejects the charge and insists its programme is for peaceful power generation only.
Ahmadinejad is in Pakistan attending a meeting with the leaders of neighbouring Pakistan and Afghanistan aimed at promoting regional stability.
"There is no fundamental problem among the countries of the region. All the problems are coming from outside," he said.