By Mitra Amiri and Hashem Kalantari
TEHRAN (Reuters) - Crowds chanted "Death to Britain" at Tehran University on Friday prayers as a hardline Iranian cleric warned the U.N. and European Union against siding with London after students and militia stormed the British embassy in Tehran.
Cleric Ahmad Khatami denounced those who tied themselves to "the rotten rope of Britain" including the EU - which may slap more sanctions on Iran over its nuclear program - as a group involved in the embassy's ransacking prepared to give Iranian diplomats expelled from Britain a hero's welcome home.
Britain evacuated its diplomats from Tehran and closed down the Iranian embassy in London after scores of Basiji militia men and radical students sacked the embassy and a residential compound on Tuesday.
In response, the biggest EU countries withdrew their ambassadors and the United Nations Security Council said it "condemned in the strongest terms" the attack.
Khatami told worshippers that the Security Council was showing itself to be as bad Britain, which Iranian hardliners believe is plotting to bring down their Islamic system.
"Issuing a statement against Iran means falling into a well with the rotten rope of Britain," Khatami said to chants of "Death to Britain."
Khatami also warned Britain's EU partners, which tightened sanctions on Tehran on Thursday and are considering banning Iranian oil imports, against closing ranks with London.
"If you have just a bit of wisdom, you won't tie your rope to the rotten rope of Britain," he said.
Rising tensions with the world's fifth biggest oil exporter pushed up global oil prices despite concerns of a sustained economic downturn in the West. Brent crude rose toward $110 a barrel on Friday.
With international pressure on Tehran rising, EU foreign ministers laid out the plans on Thursday for a possible embargo on Iranian oil in response to growing Western suspicions that the Islamic Republic aims to build nuclear weapons.
Iran says its nuclear program is peaceful but the U.N. nuclear watchdog body issued a report last month which suggested it has worked on designing an atom bomb.
Iranian diplomats expelled from London were due to arrive in Tehran in the early hours of Saturday and the Basij militia said it would have a welcoming committee for them at the International Imam Khoneini Airport outside the capital.
Iran's Foreign Ministry expressed regret over the embassy invasion which it said was a spontaneous overflowing of anger during a peaceful protest by students.
However, Britain says there must have been at least tacit approval by the ruling establishment.
Reformist website Sahamnews issued a statement by a group of students at the Islamic Azad university condemning the attack and saying the hardliners did not represent the view of most young Iranians.
"The indecent and obscene nature of this move is clear to everyone, but misusing the name of student is something we cannot easily let pass. There is no connection between what these people did and the honorable and sensible Iranian students," the statement said.
President Mahmoud Ahmadinejad has yet to comment publicly on the attack - underscoring analysts' views that the faction-driven government has mixed feelings about the event that is likely to lead to further international isolation.
Parliamentary speaker Ali Larijani, a long-time rival to Ahmadinejad, immediately condemned the U.N. reaction to the embassy storming as "hasty" and "devious."
British diplomats were evacuated after their offices and living quarters were ransacked.
The historic 135-year-old embassy residence in a wooded compound in downtown Tehran, used by the ambassador to host official dinners, was said to have been "systematically destroyed" during the onslaught.
One western diplomat who visited the scene on Thursday said priceless oil paintings has been slashed and that the protesters had cut the face out of a portrait of Queen Victoria. There were no reports of harm to diplomatic staff.
(Additional reporting by Parisa Hafezi; Writing by Robin Pomeroy; editing by David Stamp)