Japan's defense minister warned Friday that further crimes by U.S. troops here could shake the two countries' alliance, while the foreign minister said Tokyo would install security cameras around U.S. bases and take other steps to deter crime.

The warning of fraying ties by Defense Minister Shigeru Ishiba came amid a furor over troop-related crimes in Japan after a U.S. Marine's arrest last week on suspicion of raping a 14-year-old girl on the southern island of Okinawa.

"I don't think an alliance is possible unless the U.S. shares the view that if incidents like this continue to happen, it could shake the foundation of the Japan-U.S. alliance," Ishiba said during a lower house parliamentary meeting.

Ishiba urged the U.S. to take concrete prevention measures, and said promises to improve behavior in the future were not enough.

The Marine's arrest and a series of other crimes blamed on U.S. troops have heightened sentiments against the U.S. military presence in Japan, particularly on Okinawa, where more than half the 50,000 U.S. troops in the country are based.

Also Friday, Foreign Minister Masahiko Komura unveiled new security steps to curb crime around bases.

In addition to surveillance cameras, Komura announced joint Japanese-U.S. patrols of entertainment districts around bases and said the U.S. would give Japanese authorities more information about personnel living in off-base housing.

While the patrol applies to only bases in Okinawa, it was not immediately clear which areas the other measures apply to.

"We need continuous efforts for prevention of a recurrence," Komura said, adding that Japan and the U.S. will review the off-base housing policy. The Foreign Ministry said it would publicly release a list of the measures later in the day.

The U.S. this week imposed tight new restrictions on troops, their families and civilian expatriates in Okinawa and elsewhere, limiting them to bases, workplaces and off-base housing. The military held a "day of reflection" Friday to urge troops not to commit crimes.

The steps were part of a broad U.S. campaign in the past week to soothe feelings as rising anger over the alleged crimes threatened to erupt into widespread protests against the American presence.

The latest furor began last week with the arrest of 38-year-old Staff Sgt. Tyrone Luther Hadnott over the alleged rape of a 14-year-old girl on Okinawa. Police said that Hadnott admitted to investigators that he forced the girl down and kissed her, but that he insisted he did not rape her.

The tensions have been compounded in recent days by allegations of other less serious crimes such as drunken driving, trespassing and counterfeiting. Japanese leaders have deplored the behavior and accused the U.S. military of lax discipline.

Okinawa is considered a cornerstone of the U.S. military presence in Asia, and Washington is eager to quell rising negative sentiments. U.S. military officials have apologized profusely, and Ambassador Thomas Schieffer traveled to Okinawa last week to try smoothing relations.