Iranian security forces have arrested an Israeli-backed “terrorist team” that was planning attacks inside Iran, the Intelligence Ministry announced Tuesday, four days before crucial nuclear talks with world powers.

The announcement, reported by the state-run Islamic Republic News Agency (IRNA), said that “terrorists, backed by the Zionists,” were arrested after months of intelligence operations in central and border provinces and that the “Zionist regional headquarters” was discovered in another country in the region. The ministry did not specify when or where the arrests were made or say how many alleged terrorists were rounded up. In Iran’s ideological vocabulary, Israel is called the “Zionist state.”

Although the report did not name the regional country, Iranian media in recent months have quoted several officials as saying that neighboring Azerbaijan has sheltered operatives plotting attacks in Iran.

The Intelligence Ministry said security forces identified and arrested all of the team’s members before they implemented their plan, IRNA reported.

Like previous Iranian reports on arrests of spies and terrorists, Tuesday’s assertion could not be independently verified. It comes as Iran and world powers prepare to meet Saturday in Istanbul for their first nuclear negotiations in more than 13 months.

Describing firefights during some of the arrests, IRNA quoted an unidentified Intelligence Ministry official as saying that “heavy bombs, machine guns, handguns, silencers, military and telecommunications equipment and other terrorist tools” were discovered during several raids. No further details were provided.

Israel’s government declined to comment on the Iranian announcement, Israeli news media reported.

Authorities in Tehran have feared fresh assassination attempts on scientists connected to Iran’s controversial nuclear program, after four rush-hour killings of physicists and atomic experts in the past two years.

Iranian leaders have accused the United States, Britain and Israel of organizing the assassinations. Iran was also rocked last year by a series of mysterious explosions that damaged strategic gas pipelines and a key missile base. But the government has stopped short of accusing its enemies of fighting a covert war on its territory.

There have been signs, however, that Iran is increasingly involved in an intelligence cold war with the United States and its allies.

In October, U.S. officials said they had foiled a plan backed by the elite Quds Force of Iran’s Revolutionary Guard Corps to assassinate the Saudi ambassador to Washington with the help of a Mexican drug cartel. Iran denied any involvement in the alleged plot, calling it a “bad Hollywood scenario.”

According to the Associated Press and ABC News, U.S. officials in November acknowledged that dozens of operatives working undercover for the CIA had been arrested in Iran and Lebanon, with most feared dead or in prison.

In December, Iran said it had brought down an advanced U.S. stealth drone, the RQ-170 Sentinel, in its airspace. U.S. officials said the unmanned aircraft malfunctioned and crashed.