Updated

The West has begun a "heavy battle" with Iran by tightening sanctions over Tehran's disputed nuclear program, Iranian President Mahmoud Ahmadinejad said on Thursday in his first major speech since a European Union oil embargo took effect this month.

Speaking at a conference in comments to be broadcast nationwide, Ahmadinejad said his government was doing all it can to sidestep a growing list of international sanctions, imposed over Iran's refusal to halt its uranium enrichment activities.

"A heavy battle has begun by ... enemies against the Iranian nation," the official IRNA news agency quoted him as saying.

"A big part of the government is working round the clock, working every moment ... to stand up to them," he added. "The government will not retreat one iota from their rights, values and principles against weakening materialistic powers," he said.

The remarks come two weeks after a total oil embargo imposed by the European Union and banking sanctions by the U.S. went into effect against Tehran over the uranium enrichment, which it says is for peaceful purposes only but which the West says is aimed at developing weapons technology.

The latest EU sanctions on Iran's vital oil industry came into effect July 1, three days after the U.S. tightened sanctions that prohibit international banks from completing oil transactions with Iranian banks, further complicating Iran's ability to conduct trade abroad.

Economic experts say the cost of imports to Iran have increased between 20 and 30 percent because of Western sanctions.

Iran's parliament speaker has acknowledged that 20 percent of Iran's economic problems are due to sanctions, a rare public acknowledgment by a top official that sanctions are biting.

The country's powerful Revolutionary Guard has warned that Tehran would order the closure of the strategic Strait of Hormuz, the passageway through which a fifth of the world's oil flows, in retaliation if the country's oil exports were blocked.

Military leadership says that while a plan exists to block the key route, the final decision rests in the hands of the country's Supreme Leader Ayatollah Ali Khamenei.