STOCKHOLM (Reuters) - Global military spending reached a record $1,464 billion last year with the United States taking up by far the biggest share of the total, Stockholm International Peace Research Institute (SIPRI) said on Monday. Arms shipments were up 4 percent worldwide from 2007 and 45 percent higher than in 1999, the think-tank said in its annual study of the global arms trade. Last year there were around 8,400 operational nuclear warheads in the world, according to SIPRI estimates. Of them, almost 2,000 were kept on high alert and capable of being launched within minutes. Counting spare warheads, those in storage and those due for dismantlement, there were some 23,300 nuclear weapons in the arsenals of eight states: the United States, Russia, China, Britain, France, India, Pakistan and Israel, it said. The idea of the 'war on terror has encouraged many countries to see their problems through a highly militarised lens, using this to justify high military spending, Sam Perlo-Freeman, head of the Military Expenditure Project at the think-tank said in a statement. Meanwhile, the wars in Iraq and Afghanistan have cost $903 billion in additional military spending by the USA alone. The United States accounted for 58 percent of the worldwide increase between 1999 and 2008. China and Russia both nearly tripled their military spending over the decade, SIPRI said. Other countries such as India, Saudi Arabia, Iran, Israel, Brazil, South Korea, Algeria and Britain also contributed substantially to the total increase. The institute, which conducts independent research on international security, armaments and disarmament, said last years military spending comprised about 2.4 percent of global gross domestic product, corresponding to $217 per capita. US Boeing remained the top arms producer in 2007 - the most recent year for which reliable data is available - with arms sales worth $30.5 billion. All the top 20 companies among the 100 top producers in 2007 were either US or European firms, the think-tank said. The total staff involved in peacekeeping operations also reached a record high of 187,586, an increase of 11 percent from a year earlier. Despite this, some of the ambitious missions being deployed in trouble spots like Darfur and the Democratic Republic of the Congo remain far short of their envisioned strengths, SIPRI said.