"Those who say that sanctions are not important probably don't know anything about people's wallets," Rouhani said in a televised speech, adding that they had raised the cost of imported goods by 10 to 15 percent.
In recent weeks, the president's conservative critics have claimed that the main cause of Iran's economic woes is not Western sanctions imposed over its controversial nuclear programme but failings in government policy.
Tehran mayor Mohammad Bagher Ghalibaf said earlier this month that "mismanagement and a lack of planning in the current and previous governments have had more impact than sanctions".
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Parliament speaker Ali Larijani said only "20 to 30 percent of the economic problems" of the country were due to international sanctions.
Rouhani has made the quest for a deal lifting the sanctions in return for reining in Iran's nuclear programme the centrepiece of his two years in power.
Iran and world powers are working to a June 30 deadline for a comprehensive agreement.
Sanctions imposed by the European Union and the United States on Iran's oil and financial sectors since 2012 have plunged the country into a deep economic crisis with inflation rising to more than 40 percent.