Russia on Tuesday blasted unilateral European Union sanctions imposed against Iran's energy sector as "unacceptable", saying the move showed a disregard for the UN Security Council.

The angry comments from the foreign ministry underlined that Moscow is still looking after its economic interests in Iran, despite an increasingly tense relationship with the Islamic Republic's political leadership.

"We have already said many times that we consider unacceptable the practice of unilateral or collective sanctions measures against Iran, that go beyond the Security Council sanctions regime in action in the country," it said.

The statement came after EU foreign ministers on Monday formally adopted new sanctions on Iran's key energy sector, with Canada following suit, in a bid to push Tehran into talks on its controversial nuclear programme.

The measures include a ban on the sale of equipment, technology and services to Iran's energy sector, EU diplomats said. New investments in the energy sector were also banned.

The EU sanctions follow similar measures meted out by the United States.

Iran is already under four sets of UN sanctions over its refusal to heed repeated Security Council ultimatums to suspend uranium enrichment, the most controversial part of its nuclear programme.

Iran says that it is enriching uranium purely for peaceful use, but Western powers are concerned that it intends to develop a nuclear weapon.

Russia said Tuesday that the EU sanctions showed "disregard for the carefully regulated and coordinated provisions of the UN Security Council."

Russia also "categorically rejects" any attempts to use sanctions against companies and individuals from third countries who are "conscientiously carrying out the demands of UN Security Council resolutions," it said.

It said that the EU and the US by imposing additional sanctions on Iran "are showing their contempt for the principles of joint work."

Russia, traditionally a diplomatic and economic ally of Iran, in the past took a milder line against Tehran than Western powers but recently has noticeably hardened its position, sparking anger in Tehran.

President Dmitry Medvedev declared earlier this month that Iran was close to having the potential to build a nuclear weapon, the first time a Russian leader had warned so explicitly of the dangers of the Iranian nuclear programme.

But there have also been signs Moscow is keen to retain its economic ties with Tehran.

Energy ministers of the two countries met earlier this month with energy-hungry Iran winning a pledge from Moscow to supply fuel, despite unilateral US and EU sanctions targeting its energy sector.

Moscow is also helping Tehran build its first nuclear power station in the southern city of Bushehr in a project that does not fall under the UN sanctions.

The construction of the power plant is on schedule and preparatory work should be completed before September, a Russian official said Tuesday.

"As was planned, by the end of August all work for the first stage of the physical launch should be completed," the head of Russia's nuclear agency Sergei Kiriyenko said according to RIA Novosti.

Russia is "blowing hot and cold on Iran" by backing UN sanctions but continuing economic collaboration, said Masha Lipman, a political analyst at the Carnegie Moscow Centre.

"There are people in Russia who are unhappy about Russia's rapprochement with the US on Iran and Ahmadinejad is playing on disagreements within the elite."

Russia has "run out of patience" with Iran, but sees US and EU sanctions as breaking international law, said Fyodor Lukyanov, editor of Russia in Global Affairs journal.

"Russia feels that its opinion is being overlooked."