Iran will not abandon or modify its regional policies in exchange for Western concessions to seal a deal on its nuclear programme, analysts say.
General Qassem Soleimani, a commander of Iran's elite Revolutionary Guards, in February hailed Tehran's widening influence from "Bahrain to Iraq, and Syria to Yemen and North Africa".
Tehran says it supports Iraq against Islamic State (IS) jihadists by providing weapons, equipment and military advisers.
Even the US military's top officer, General Martin Dempsey, said the role of Iran and Shiite militias in this week's Iraqi offensive to retake the city of Tikrit from IS extremists could be positive, provided it did not fuel more sectarianism.
But the West and Gulf monarchies are concerned by Iran's growing influence in other countries of the region.
Tehran is a key ally of the Syrian regime against the armed opposition, and it is accused of supporting Shiite-led protests against the Sunni dynasty ruling Bahrain and of having contributed to the seizure of power by Shiite rebels in Yemen.
Iran provides financial and military assistance to Palestinian armed groups, including the Islamist movement Hamas which controls Gaza, and the powerful Shiite group Hezbollah in Lebanon.
Washington has said it will "confront aggressively" any bid by Iran to expand its regional influence on the ground even if a nuclear deal is struck.
On Tuesday, Israeli Prime Minister Benjamin Netanyahu denounced the Islamic republic's regional ambitions and its threats against Israel, in a bid to torpedo any deal on its nuclear programme.
Iranian foreign ministry spokeswoman Marzieh Afkham countered that Iran "is a real and substantial power in the region and wants to use its influence to ensure peace, security, stability and progress".
As for any linkage, she said "no other business" was being discussed with world powers.
Ali Vaez, Iran specialist at the International Crisis Group, confirmed that the nuclear standoff and regional issues were not connected.
The major powers and Iran "have seriously negotiated on the former, but only exchanged views on the latter", he told AFP.
"No amount of regional cooperation could change the parties' red lines on 'breakout time' (required for Iran to build an atomic bomb) and the lifting of sanctions."
Vaez said that only after a deal could Tehran and the world powers "be in a better position to try to resolve their differences".
Iranian political analyst Amir Mohebian was categorical that there is "no way Tehran will agree to negotiate on its power".
"The only power that fights Daesh (Arabic acronym for IS) on the ground today, is not the international coalition led by the United States, but Iran," he told AFP.
And "no official is allowed and will allow himself to negotiate on the power of Iran".
He denounced what he termed the US lack of strategy in Syria for "wanting (President Bashar al-) Assad to go without thinking about what happens afterwards", leaving the way open for IS.
"Why do you want Iran to change its policy today? It was right from the start," he said, echoing the official Iranian line.
Mohammad Sedghian, director of the Tehran-based Arabic Centre for Iranian Studies, underlined that it was also unthinkable for Iran to abandon its support for anti-Israeli groups.
"Iran's support for resistant movements against occupation ... whether in Palestine or Lebanon is a strategic issue ... and will not be influenced by political or economic circumstances," he said.