U.S. security officials are investigating a recent intelligence report that a group of 25 Chechen terrorists illegally entered the United States from Mexico in July.
The Chechen group is suspected of having links to Islamist terrorists seeking to separate the southern enclave of Chechnya from Russia, according to officials familiar with intelligence reports.
Members of the group, said to be wearing backpacks, secretly traveled to northern Mexico and crossed into a mountainous part of Arizona that is difficult for U.S. border security agents to monitor, said officials speaking on the condition of anonymity.
The intelligence report was supplied to the U.S. government in late August or early September and was based on information from an intelligence source that has been proved reliable in other instances, one official said.
A second U.S. official said the report is being investigated, but said it could not be determined whether the group of Chechens actually entered the country, as the intelligence source reported.
"We don't know whether or not that report is true," this official said.
A spokesman for U.S. Customs and Border Protection confirmed that the intelligence report was provided by another government agency, but said Border Patrol agents were unable to verify its accuracy.
It could not be learned whether the reported infiltration is related to the recent Education Department warning to school officials to examine security in the aftermath of the attack last month by pro-Chechnya Muslim terrorists on a school in Russia, in which more than 300 people were killed and some 700 wounded.
In the Russian attack, heavily armed Islamists took over and wired with explosives the school building in Beslan, North Ossetia. It is believed that an accidental explosion set off a battle between Russian security personnel and the terrorists, who set off several explosions and shot schoolchildren and teachers as they tried to escape.
U.S. officials believe the Beslan terrorists included some al Qaeda-linked foreign terrorists.
The Education Department letter said that school officials should examine "protective measure guidance" for helping to prevent and respond to a similar terrorist attack, were it to occur in the United States.
The notice said the FBI and the Department of Homeland Security are "currently unaware of any specific, credible information indicating a terrorist threat to public and private schools, universities or colleges in the United States."
The letter stated that indicators of terrorist surveillance before an attack include interest in site plans for schools, bus routes and attendance lists from persons who don't normally request such information.
Authorities also were advised to remain alert for "static surveillance" by people who may be disguised as panhandlers, shoeshiners, newspaper or flower vendors, or street sweepers who seem out of place in a particular area.
Other indicators of terrorist surveillance can include spying on school security drills, people staring at employees or vehicles in parking areas, and surveillance by pedestrians.
Fears of an attack on American schools also were raised by the recent discovery in Iraq of a computer disk containing data showing the layout of six schools in the United States, including districts in California, Florida, Georgia, Michigan, New Jersey and Oregon.
Officials believed the disk may have been part of a terrorist plot. However, FBI officials said on Friday that there did not appear to be a terrorist threat connected to the computer disk.
The Iraqi who had the disk, a member of Saddam Hussein's Ba'ath Party, apparently was collecting information from the Internet sites of American schools that would be useful for emergency planning for Iraqi schools, U.S. officials said.
U.S. security officials have been concerned in recent months that al Qaeda or other terrorists are planning to enter the United States from Mexico.
Intelligence officials said a suspected al Qaeda leader who has been in the United States was spotted recently in Mexico. Officials believe Adnan Shukrijumah, whom the FBI wants for questioning, met with alien smugglers in Mexico and Honduras and was seeking ways to bring al Qaeda members into the United States. Shukrijumah was seen in August in the Sonora province of northern Mexico, officials said.
Since October 2003, authorities have arrested five Arabs attempting to cross illegally into the United States from Mexico.
In July, officials dismissed as untrue an Internet report that said a group of Middle Eastern men were recently caught trying to cross the border from Mexico.
The report apparently was based on a group of Oaxacan tribesmen who were stopped as they tried to cross the border in Arizona. The tribesmen spoke an Indian language native to southern Mexico that may have been mistaken for Arabic, officials said at the time.

The intelligence report was supplied to the U.S. government in late August or early September and was based on information from an intelligence source that has been proved reliable in other instances, one official said.