Italian authorities arrested four Moroccans in a raid on a Rome apartment where they found maps detailing the U.S. Embassy and a substance apparently containing small quantities of cyanide, officials said Wednesday.

Chief Prosecutor Salvatore Vecchione said the substance was undergoing analysis and appeared to be potassium ferrocyanide — a common industrial chemical used in the production of wine and ink dye, among other things. Small amounts of cyanide can be extracted from it, but with great difficulty.

In Washington, State Department spokesman Richard Boucher thanked the Italian government.

"Because of their ongoing commitment to countering the terrorist threat, Italian authorities have repeatedly thwarted planned terrorist attacks against American and other targets inside Italy. The latest incident shows the continuing danger posed by terrorists and the need to remain at a high level of vigilance, and we will do that."

In January 2001, the embassy was closed to the public for three days because of a terrorist threat that was later linked to Al Qaeda. Boucher said the embassy would remain open this time.

"We're carefully reviewing security measures and taking all appropriate precautions. At this point we don't see an immediate threat to the embassy or embassy employees."

The arrests took place in a pre-dawn raid on the outskirts of Rome Tuesday and were leaked to Italian media, which also reported that the maps found in the apartment included details of the city's water system.

The AGI news agency said the suspects were part of the Salafist Group for Call and Combat, an Algerian organization allegedly financed by Usama bin Laden. Shortly after Sept. 11, Spain arrested six Algerians suspected of belonging to the dissident group.

Other reports in Italy Wednesday linked at least one of the suspects there to a terrorist cell in Milan suspected of having links to bin Laden's Al Qaeda network. The cell was apparently dismantled last year with the arrest of seven Tunisians now on trial in Milan. In wiretapped phone conversations, the Tunisians appeared to be speaking in code about cyanide, Italian officials have said.

Officials refused to comment on most of the reports and Vecchione said his office was investigating the media leaks. He would not go beyond confirming the arrests and the discovery of maps, false documents and the chemical substance.

An official who spoke on condition of anonymity however said the U.S. Embassy was circled on the maps.

News reports said investigators believed the suspects planned to contaminate the water supplies in the capital, including the commercial area around Via Veneto where the U.S. Embassy is located.

Col. Gianfranco Cavallo of the Carabinieri paramilitary police declined to comment on the reports.

Embassy officials publicly thanked Italian police and security forces for "excellent work concerning the most recent security threat against the embassy" but said that "it would be premature to comment any further" since the case was under investigation.

Tuesday's raid was described as the biggest probe so far into suspected Islamic terrorist activity in the city. Three other Moroccans were arrested in the capital last week as part of the same investigation, according to Italian reports.

In Azerbaijan on Wednesday, six men went on trial accused of plotting terror attacks on the U.S. Embassy and offices of international organizations.

The Azerbaijan National Security Ministry says that the five Azerbaijanis and one Ukrainian citizen are affiliated with the Hizb-ut-Tahrir group, which has adherents throughout the Middle East and ex-Soviet states in Central Asia.

The group recently circulated leaflets denouncing the U.S.-led actions in Afghanistan and has called for creating an Islamic state in Central Asia.

The six defendants, who were arrested last month, are charged with preparing for terror attacks and plotting to overthrow the government.

The ministry did not say when the attacks were planned or which international offices were targeted. Prosecutors said authorities found home-made explosives, instruction manuals and extremist literature in the apartments of Hizb-ut-Tahrir members.