"I'll tell you, they are not concerned with nuclear programmes ... They are themselves engaged in nuclear activities and they are expanding day by day. They test new brands of weapons of mass destruction every day," Mahmoud Ahmadinejad said in Jakarta on Wednesday.
"Big powers pretend [they] are concerned, but it's a big lie," he said after meeting his Indonesian counterpart, Susilo Bambang Yudhoyono.
Iran is under pressure to curb a nuclear programme it says is for peaceful purposes but which the West sees as a potential weapons threat.
The US has pushed for international action on the issue, and with a group of nations including China and Russia has authorised Britain, France and Germany to work on a package to entice Iran to change its programme.
Ahmadinejad said the Iranian people resented "incorrect decisions" taken by the international community.
"The Iranian people are capable of defending their own rights and interests," he said.
"The resistance of the Iranian people is not only in defence of the rights of the Islamic world but also the rights of all the people in the world.
Ahmadinejad (L) with Yudhoyono
in Jakarta on Wednesday
"We think that this is the right of every nation: to use modern science and technology, and the right has been enshrined in the provisions of the NPT [Non-Proliferation Treaty]."
Earlier, Indonesia warmly welcomed Ahmadinejad as he began a five-day trip. He received a 21-gun salute and reviewed a military honour guard in Jakarta, the capital city.
Ahmadinejad stood next to Yudhoyono on a reviewing stand in the grounds of the presidential palace as their national anthems were played.
Media Indonesia newspaper quoted Hassan Wirajuda, Indonesia's foreign minister, as saying on Tuesday that the visit "will be the first opportunity for us to hear directly about Iran's response to the solutions that have been proposed" on the nuclear issue.
Wirajuda, asked if Iran's nuclear programme would be raised in bilateral talks, said: "Certainly it will be discussed, it's an important issue."
Ahmadinejad will travel to Bali to
attend a meeting of leaders
Wirajuda said: "We support the development of nuclear programmes for peaceful purposes. This is the sovereign right of every nation. But we have been consistently against the proliferation of nuclear weapons."
The prime purpose of Ahmadinejad's visit is supposed to be the development of economic ties.
Iran is investing several billion dollars in the oil and gas sector of Indonesia, a fellow Opec member, and both countries want to increase trade.
Indonesia's government, walking a tightrope between friendship with the West and a political need not to offend the country's overwhelming Muslim majority, is unlikely to push Ahmadinejad very hard on the nuclear issue.