He urged EU countries to follow the US in freezing Iranian central bank assets and imposing an embargo on oil exports.
Iran has dismissed the threat of sanctions. On Tuesday, it denied that a record low of its currency was linked to US punitive measures.
It also denies Western charges that it is trying to develop nuclear weapons.
Tehran says its programme is peaceful – it needs nuclear technology to generate electricity to meet growing domestic demand.
In November, the US, Canada and the UK announced new sanctions against Iran in the wake of the report from the UN nuclear watchdog, the International Atomic Energy Agency (IAEA), that said Iran had carried out tests related to “development of a nuclear device”.
But Iran was not referred to the UN Security Council because Russia and China were opposed to the move.
“Iran is pursuing the development of its nuclear arms, I have no doubt about it,” Mr Juppe told French television I-Tele.
“The last report by the International Atomic Energy Agency is quite explicit on this point.”
Mr Juppe said France wanted the sanctions against Iran toughened further.
He said President Nicolas Sarkozy had already proposed “the freezing of Iranian central bank assets, a tough measure, and the second an embargo on Iranian oil exports”.
“We want the Europeans to take a similar step by January 30 to show our determination,” he said.
The UN Security Council has already passed four rounds of sanctions against Iran for refusing to halt uranium enrichment.
Highly enriched uranium can be processed into nuclear weapons.
The US had already sanctioned dozens of Iranian government agencies, officials and businesses over the nuclear programme.
The government in Tehran has dismissed the latest measures announced in the wake of the IAEA report in November.
Since then, however, the Iranian national currency, the rial, has lost about 12% of its value – trading at about 17,200-18,000 rials to $1.
Reuters news agency said some exchange offices in Tehran said they had suspended trading until further notice.
“The rate is changing every second… we are not taking in any rials to change to dollar or any other foreign currency,” the agency quoted Hamid Bakhshi as saying.
But the government said the dip was not linked to the latest US sanctions targeting the central bank.
Foreign ministry spokesman Ramin Mehmanparast said the US sanctions “have yet to be put into practice”.
Iran has also been holding a series of naval exercises in the Gulf, and on Monday said it had successfully test-fired a surface-to-sea Qader cruise missile, a shorter range Nasr and later, a surface-to-surface Nour missile.
A medium-range surface-to-air missile was successfully launched on Sunday, Iranian media reported.
Iran has conducted 10 days of exercises near the Strait of Hormuz, through which 20% of the world’s oil passes.
Tehran said on Monday that “mock” exercises on shutting the strait had been carried out, although there was no intention of closing it.
The BBC’s Iran correspondent James Reynolds says Iran is using the exercises to try to show that it owns the Gulf and has the military capability to defend any threat to its dominance.
But, says our correspondent, few believe Iran would carry out its threat to shut the Strait of Hormuz as to do so would be considered too economically, politically and possibly militarily damaging for Tehran.