NUEVO LAREDO, Mexico (AP) - The streets around the U.S. Consulate in this bustling border town usually teem on weekdays with Mexicans who want visas to cross the Rio Grande to visit the United States.

But on Thursday, the well-worn sidewalks around the consulate were empty except for the armed guards standing watch. The consulate's visa section, one of the busiest in the world, was closed a day earlier because of evidence that workers there were illegally selling entry permits.

Thomas Armbruster, consul general in Nuevo Laredo, said the visa section would remain closed at least through next week. The consulate continues to provide its usual services to U.S. citizens, he said.

Armbruster said all 30 or so Mexican citizens who work at the consulate are on administrative leave until Monday. Those workers have been interviewed by U.S. investigators called in from Washington, Mexico City and Monterrey.

"We felt that it was a problem that was bigger than something that we could identify all the facets of locally," said Armbruster, who has been the consul here for more than two years.

He wouldn't identify what specifically triggered suspicions within the consul, saying only that irregularities were observed. He wouldn't say how many people may be involved or the number of illegal visas that may have been issued.

Armbruster said the consulate typically interviews 300 to 400 visa applicants a day.

While the consulate's visa office is closed, applicants from the border region are being sent to consulates in Monterrey and Matamoros.

Armbruster would not say whether there were concerns about illegal visas being issued to Middle Eastern men or others subjected to closer scrutiny for entry to the United States since the Sept. 11 attacks.

Armbruster said the consul's U.S. staff expected to be briefed by investigators in the next few days, at which time they may determine which workers may have participated.

He said the probe by the State Department and the Justice Department has been under way for many months.

"What investigators are looking for is the evidence they need to prosecute, and I think that's what slows the process down," he said.

Where any prosecutions might take place was unclear Thursday. Nancy Herrera, a spokeswoman for the U.S. Attorney's Office in Houston, would not speculate about charges that could be filed or how criminal charges arising from the illegal visa investigation might be handled.

"Corruption in the Consulate," screamed a bold front-page headline in Thursday's edition of the Nuevo Laredo newspaper El Manana.

The newspaper quoted unnamed Mexican government sources as saying that the five people -- two Mexicans and three Americans -- had been detained. Herrera said she was not aware of anyone being charged in the visa case.

Each day thousands of people either drive or walk across the three bridges spanning the Rio Grande between Nuevo Laredo and Laredo, Texas.

Ramon Juarez, Laredo port director for the U.S. Immigration and Naturalization Service, said Thursday that the visa shutdown in Nuevo Laredo has so far had no noticeable effect on the number of people crossing over from Mexico.

"But if it were to go on for quite some time, there might be an impact," he said.