About 30 detainees from the U.S. war on terrorism arrived Monday at the U.S. Naval base at Guantanamo Bay, Cuba.

A plane carrying the detainees from an unidentified location landed at the base Monday morning, Pentagon spokeswoman Lt. Cmdr. Barbara Burfeind said in a telephone interview from Washington.

She said the new arrivals boost the number of detainees at the seaside Camp Delta to "approximately 625." She would not go into specifics nor give the detainees' nationalities.

There were 598 men from 43 countries held at Guantanamo before four were released over the weekend.

Meanwhile, the Pentagon confirmed its first release of prisoners no longer considered a threat.

The International Committee of the Red Cross said three Afghan citizens from Guantanamo arrived Sunday at the U.S. military headquarters at Bagram air base, in Afghanistan, and Pakistan confirmed the arrival of one of its citizens.

U.S. officials determined the four "no longer posed a threat to U.S. security," Pentagon spokeswoman Virginia Clarke said.

Military authorities in Guantanamo have released little information about the detainees in recent months, save to say that some have tried to commit suicide. Earlier this month, about 50 were in solitary confinement and 26 were taking antidepressants or anti-psychotic drugs.

Secretary of Defense Donald H. Rumsfeld has said detainees could be tried by tribunals or other courts, sent home for prosecution, released or held indefinitely at Guantanamo. The detainees have not been charged and are not allowed lawyers as they undergo interrogations.