Democracy and democratic elections are attainable by reference to the people's vote and respect to the law, he told reporters.
During Ahmadinejad's administration, Iran faced heavy worldwide sanctions for its nuclear program, which Western countries said aimed to develop weapons.
He registered to run on the same day as did his former Vice President Hamid Baghaei, saying at the time his decision was meant to support his political ally. Others include a brother of late President Akbar Hashemi Rafsanjani and Tehran's mayor.
Nearly all will be disqualified over the coming fortnight by the Guardian Council, which is controlled by religious conservatives. The clerical Guardian Council will vet the candidates and publish the final list on April 27, removing most dissidents.
Ellie Geranmayeh, a senior policy fellow for the Middle East and North Africa program at the European Council for Foreign Relations, told Bloomberg that despite sanctions against Iran being lifted, "people are not seeing a huge elevation for Iran in terms of the economy or its place on the worldwide stage". The council, which is made up of clerics and Islamic jurists, normally disqualifies dissidents, women, and many reformists.
Ahmadinejad also voiced reluctant support for Iran's 2015 nuclear deal with the USA and other world powers, which saw Iran accept curbs on its nuclear program in exchange for relief from crippling global sanctions.
Since the deal, Iran has signed multi-billion-dollar contracts with airplane manufacturers Boeing Co. and Airbus.
But despite months of talks, hardliners have been unable to unite behind a single candidate, and Khamenei has not yet intervened to make them do so.
"With the deal in jeopardy, the system will be in vital need of Rouhani's team of smiling diplomats and economic technocrats to shift the blame to the USA and keep Iran's economy afloat", said Iran analyst Ali Vaez of the International Crisis Group. As a former prosecutor, head of the Iranian judiciary, and attorney general, the well-known cleric has established hardline credentials, and his economic policy seems to reflect the preoccupations shared by Rouhani's declared opponents and the supreme leader.
Earlier on Friday, the Fars news agency reported that Rouhani had registered to run for re-election.
Rouhani also mentioned the giant joint gas field, the North Field, Iran will be developing with Qatar. If you would like to discuss another topic, look for a relevant article.
"He will go until the end", Javanfekr said.
A third prominent contender is the former president Mahmoud Ahmadinejad.
"I think definitely it has complicated the race", Ansari said.
"It was very weird, but it could be entertainment for people", 31-year-old nurse Roya Khani said.