The announcement tops Iran's declaration last month when it said it had surpassed the 3.6 percent level.
Uranium enriched to between 3.5 and 5 percent is used to make fuel for reactors to generate electricity. Enriched to more than 90 percent, it becomes suitable for use in nuclear weapons.
"The latest enrichment percentage carried out in Iran is 4.8 percent," state-run television quoted Aghazadeh as saying.
Aghazadeh added that Iran has no intention of enriching uranium beyond 5 percent.
Aghazadeh also announced the discovery of uranium deposits in southern Iran near the port city of Bandar Abbas.
Iran announced April 11 that it had enriched uranium for the first time.
The Security Council has demanded that Iran cease all of its enrichment-related activities until Tehran answers its questions on its nuclear program.
Last week, the International Atomic Energy Agency reported that Iran flouted the council's requests.
Iran says its nuclear program is confined to generating power, but the United States and France accuse the country of secretly trying to build nuclear weapons.
Mohammad Ghannadi, deputy chief for nuclear research and technology, told a conference in Qom, south of the capital Tehran, Tuesday that the country's political leadership had ordered him to ensure that enrichment did not go beyond 5 percent.
"We need enriched uranium to produce electricity ... we have been given orders to enrich uranium only up to 5 percent," he said.
Aghazadeh, the nuclear chief, said studies show there are considerable amounts of uranium ore at Bandar Abbas.
"The deposits have not been identified fully but studies show that there are considerable amounts of uranium (ore) at the site," he said adding that additional exploration at the site was underway," television quoted Aghazadeh as saying.
The announcement of the deposits came just after Ghannadi, the deputy, said Tuesday that Iran had discovered uranium ore at three new sites in the central Khoshoomi, Charchooleh and Narigan areas.
Aghazadeh, who is also the head of Atomic Energy Organization of Iran, said Iran was planning vast investments to extract uranium from its deposits.
"Experts at the (Iran's) Atomic Energy Organization are making plans to identify the country's uranium reserves. It is predicted that we will have vast investments in various parts of the country," he said.