The three countries' foreign ministers said they would continue to seek "a new diplomatic solution to ensure Iran never gets a nuclear weapon".
"The reimposition of UN sanctions is not the end of diplomacy," the foreign ministers of the three European nations, known as the E3, said in a joint statement.
"We urge Iran to refrain from any escalatory action and to return to compliance with its legally binding safeguards obligations," they said.
Iran recalled its envoys from Britain, France and Germany for consultations on Saturday, state television reported.
Iran on Sunday condemned as "unjustifiable" the reinstatement of United Nations sanctions over its nuclear programme, after the collapse of talks with Western powers and Israeli and US strikes on its nuclear sites.
The measures, which bar dealings linked to the Islamic republic's nuclear and ballistic missile activities, took effect overnight after Western powers triggered the so-called "snapback" mechanism under the 2015 nuclear accord.
"The reactivation of annulled resolutions is legally baseless and unjustifiable... all countries must refrain from recognising this illegal situation," the Iranian foreign ministry said in a statement.
"The Islamic Republic of Iran will firmly defend its national rights and interests, and any action aimed at undermining the rights and interests of its people will face a firm and appropriate response," it added.
The return of the sanctions ends months of tense diplomacy aimed at reviving nuclear talks derailed since June, when Israeli and US forces bombed Iranian nuclear facilities.
Despite the reimposition, Western leaders stressed channels for dialogue remained open.
Kaja Kallas, the European Union's top diplomat, on Sunday said the reimposition of sanctions "must not be the end of diplomacy", adding that "a sustainable solution to the Iranian nuclear issue can only be achieved through negotiations".
Economic impact
The sanctions are a "snapback" of measures frozen in 2015 when Iran agreed to major restrictions on its nuclear programme under a deal negotiated by former president Barack Obama.
The United States already imposed massive sanctions when President Donald Trump withdrew from the deal in his first term.
Iran and the United States had held several rounds of Omani-brokered talks earlier this year before they collapsed in June when first Israel and then the United States attacked Iranian nuclear facilities.
On the ground, Iranians lamented the likely impact of the new sanctions on an already squeezed economy.
"The current (economic) situation was already very difficult, but it's going to get worse," said an Iranian engineer who asked to be identified only by his first name Dariush.
"The impact of the renewed sanctions is already evident: the exchange rate is increasing, and this is leading to higher prices," the 50-year-old said, complaining that the standard of living is "much lower" than it was two or three years ago.
The economic strain was underscored on Sunday when the Iranian rial plunged to a record low against the US dollar on the black market, trading at around 1.12 million per dollar, according to the currency-tracking websites Bonbast and AlanChand.
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