LONDON — The overall amount of money invested in soldiers, weapons and war has been largely unaffected by the global economic downturn, a think tank said in a report published today.

The London-based International Institute for Strategic Studies said the total amount of money spent on world defense budgets rose from $1.3 trillion to $1.55 trillion between 2006 and 2008, and likely continued to climb further in 2009.

The rise, however, may not be as significant as the figures suggest because they reflect the effects of the fluctuating dollar, according to the think tank.

Calculated in terms of its proportion to global GDP, military spending has remained steady in the past few years — 2.56 percent of global GDP in 2008, compared to 2.6 percent in 2004.

Key countries accounting for the biggest share of global military spending — China, U.S., France and Japan — have, in general, increased spending or kept their budgets unchanged, with Russia the only leading country making a small reduction in spending.

SHAHI KOTO, Pakistan — A roadside bomb killed three U.S. soldiers and flattened a girls' school in northwest Pakistan today in an attack that drew attention to a little-publicized American military training mission in the al-Qaida and Taliban heartland.They were the first known U.S. military fatalities in Pakistan's lawless tribal regions near the Afghan border, and a major victory for militants who have been hit hard by a surge of U.S. missile strikes and a major Pakistani army offensive.The blast also killed three schoolgirls and a Pakistani soldier who was traveling with the Americans. Two more U.S. soldiers were wounded, along with more than 70 other people, mostly students.

BAGHDAD — A bomb planted on a parked motorcycle exploded today on the outskirts of the holy city of Karbala, killing at least 20 Shiite pilgrims and wounding more than 100 others amid tight security for the huge religious procession, officials said.The blast was the latest in a string of attacks this week that have targeted pilgrims making their way to an important Shiite religious observance in Karbala, raising fears of a spike in attacks by suspected Sunni insurgents when the pilgrimage culminates Friday.For years, the main Shiite pilgrimages have been a prime target for attacks blamed on Sunni extremists seeking to widen sectarian rifts. The current processions have brought hundreds of thousands of people streaming toward Karbala to end the 40-day mourning period marking the death of Hussein, a revered Shiite figure from the 7th century.Trial for accused Nazi guard postponedMUNICH — John Demjanjuk's trial in Germany was postponed today after doctors reported the 89-year-old defendant was experiencing medical problems.The retired U.S. autoworker is being tried on accusations he was the accessory to the murders of 27,900 people while allegedly serving as a guard at the Sobibor death camp. The Ukrainian-born Demjanjuk rejects the charges, saying he was never a guard at any Nazi camp.