"It is clear to us that Iran bears responsibility for this attack. There is no other plausible explanation," Britain, France and Germany said.
Britain, Germany and France backed the United States and blamed Iran on Monday for an attack on Saudi oil facilities, urging Tehran to agree to new talks on its nuclear programme.
The Europeans issued a joint statement after British Prime Minister Boris Johnson, German Chancellor Angela Merkel and French President Emmanuel Macron met at the United Nations on the sidelines of the General Assembly.
But Iran ruled out the possibility of negotiating a new deal with powers, Iranian Foreign Minister Mohammad Javad Zarif tweeted on Monday, saying European partners have failed to fulfill their commitments under a 2015 nuclear pact.
Europe's push to defuse tensions
European leaders have struggled to defuse a brewing confrontation between Tehran and Washington since US President Donald Trump quit a deal last year that assures Iran access to world trade in return for curbs on its nuclear program.
The United States reimposed sanctions on Iran and sharply tightened them. Iran has responded by gradually breaching nuclear commitments made in the 2015 accord and has set an October deadline to further scale back its nuclear obligations unless the Europeans salvage the pact by shielding Tehran's economy from US penalties.
"The time has come for Iran to accept negotiation on a long-term framework for its nuclear programme as well as on issues related to regional security, including its missiles programme and other means of delivery," Britain, France and Germany said.
Tensions rose on September 14 following an attack on Saudi Arabia's oil facilities, which Riyadh and Washington have blamed on Iran.
Tehran denies responsibility, and Yemen's Iran-aligned Houthi group, which has been battling a Saudi-led military coalition, has said it carried out the attack.
"It is clear to us that Iran bears responsibility for this attack. There is no other plausible explanation. We support ongoing investigations to establish further details," Britain, France and Germany said.
Macron has led a European push over the summer to find a compromise between the United States and Iran and wants to use the UN meeting as an opportunity to revive diplomacy, though his efforts have stalled in recent weeks.
When asked about Macron's attempt to mediate, US President Donald Trump said: "We don't need a mediator. ... They (Iran) know who to call."
Chances of a Trump-Rouhani meeting appear slim
Trump flirted with meeting Iranian President Hassan Rouhani while both are in New York for the UN General Assembly, but the chances appear slim.
"We haven't received any requests this time, yet, for a meeting and we have made it clear a request alone will not do the job," Iranian Foreign Minister Zarif told reporters in New York earlier on Monday.
"A negotiation has to be for a reason, for an outcome, not just for a handshake."