Kuwait has arrested up to four members of its armed forces who are suspected of plotting to attack allied troops, a Kuwaiti military spokesman said.

Kuwait (search) has witnessed several small-scale attacks on U.S. troops and civilians in the past three years. But this is the first time in many years that serving members of the armed forces have been detained on such charges.

"The security apparatus in Military Intelligence is investigating some officers following information that they intended to work against friendly troops," Brig. Youssef al-Mullah said Monday.

"They are fewer than five," al-Mullah said, adding they were arrested late last week. "A number have been released after investigation."

He would not say how many remained in custody. Nor would he identify the troops they were suspected of plotting against. But the targeted troops are believed to be American.

The United States stations several thousand troops in Kuwait and used the oil-rich country to launch its March 2003 invasion of Iraq. Kuwait continues to serve as a staging ground for U.S. troops and equipment going into Iraq.

"It is just an investigation," al-Mullah said. "The military judicial proceedings will take their course."

Al-Mullah gave no further details.

The U.S. Embassy in Kuwait warned American citizens Dec. 15 that it had "credible information that terrorist groups are developing near-term plans for attacks against unspecified targets in Kuwait." The embassy urged nationals to exercise caution and report any suspicious activity.

Kuwait has stepped up its internal security in recent days, stationing armed military and police vehicles at street junctions, hotels and embassies.