TEHRAN, Iran - Iran said yesterday that a newly built U.N. station to detect nuclear explosions was set up near its border so that world powers could spy on the country.

The accusation underscored the growing bitterness in Tehran's relations with the West but puzzled the U.N. commission that approved the station. A spokeswoman said the decision was made more than a decade ago with Iran's involvement.

Construction was completed last week on the seismic monitoring station in Turkmenistan, a few miles from its Iran border. It is one of 275 such facilities around the world to detect seismic activity set off by blasts from nuclear tests - such as ones in recent years by North Korea.

Iran protested the facility even though it asserts it is not trying to produce nuclear arms. Tehran has been resisting heavy pressure in recent months to sign on to a U.N.-backed plan aimed at thwarting any attempt to build atomic weapons.

Abolfazl Zohrehvand, an adviser to Iranian nuclear negotiator Saeed Jalili, said the international treaty that allows for setting up such observatories is an "espionage treaty."

"With the disclosure of the identity of such stations, it is clear the activity of one of them [in Turkmenistan] is to monitor Iran," Zohrehvand told the state news agency IRNA.

The network of sensors is not aimed at particular countries, said Annika Thunborg, a spokeswoman for the Vienna-based Preparatory Commission for the Comprehensive Nuclear-Test-Ban Treaty Organization, or CTBTO.

There are three stations inside Iran - in Tehran and the southern towns of Shushtar and Kerman, she said.

"Iran is a member state of the CTBTO, together with 181 other countries, and is party to the decisions made by the CTBTO," Thunborg said. She noted that North Korea's nuclear blasts in May and in 2006 were detected by 23 CTBTO stations worldwide, including one in far-away Bolivia.

The commission announced last week on its Web site that the new nuclear warning station has been set up between Turkmenistan's Karakum Desert and Kopet mountain range. It said the station is undergoing testing.

The United States and some of its allies suspect Iran's announced nuclear-power program is a cover for secretly developing nuclear weapons.

Iran has balked at a U.S.-backed U.N. proposal under which it would send most of its current stockpile of low-enriched uranium to Russia and France to be processed into fuel for civilian uses and returned to it.

The proposal is aimed at easing Western concerns about Iran's nuclear program by drastically reducing its ability to enrich uranium to levels high enough to make nuclear weapons.

Iran instead defiantly announced it intends to build 10 more uranium-enrichment sites.

That statement drew a forceful rebuke from the U.N. nuclear watchdog agency, and the United States and its allies are threatening to impose more sanctions on Iran if it does not cooperate.