The US has successfully struck a disabled spy satellite with a missile fired from a warship in waters west of Hawaii, military officials say.
Operatives had only a 10-second window to hit the satellite - USA 193 - which went out of control shortly after it was launched in December 2006.
Officials were worried its hydrazine fuel could do harm, but it is not yet known if the fuel tank was destroyed.
The controversial operation has been criticised by China and Russia.
On Thursday, China called on the US to provide more information about the mission.
Russia suspects the operation was a cover to test anti-satellite technology under the US missile defence programme.
The US denies the operation was a response to an anti-satellite test carried out by China last year, which prompted fears of a space arms race.
The BBC's Jonathan Beale in Washington says this operation was hugely ambitious.
Owner: National Reconnaissance Office
Launched: 14 Dec 2006
Weight: 2,300 kg (5,000lbs)
1,134kg (2,500lbs) could survive re-entry
Carrying hydrazine thruster fuel
The operation went ahead hours after the space shuttle Atlantis landed, removing it as a safety issue for the military.
The satellite - believed by some commentators to be a radar imaging reconnaissance satellite - was passing about 130 nautical miles (250km) over the Pacific.
Earlier the military said it would use an SM-3 missile fired from the cruiser USS Lake Erie, which is posted on the western side of Hawaii along with the destroyers USS Decatur and USS Russell.
But it is not yet known how successful the operation was - the missile needed to pierce the bus-sized satellite's fuel tank, containing more than 450kg (1,000lbs) of toxic hydrazine, which would otherwise be expected to survive re-entry.
The Pentagon said confirmation that the fuel tank has been hit should be available within 24 hours.
US officials said without an attempt to destroy the fuel tank, and with the satellite's thermal control system gone, the fuel would now be frozen solid, allowing the tank to resist the heat of re-entry.
If the tank were to land intact, it could leak toxic gas over a wide area - harming or killing humans if inhaled, officials had warned.
Officials expect that over 50% of the debris will fall to Earth within the first 15 hours after the strike - or within its first two revolutions of Earth.
USA 193 lost control a few hours after launch on a Delta II rocket
Left to its own devices, about half of the spacecraft would have been expected to survive the blazing descent through the atmosphere, scattering debris in a defined "corridor" which runs across the Earth's surface.
Professor Richard Crowther, a space debris expert with the Science and Technology Facilities Council (STFC), said that if struck with the missile, about 25% of USA 193 is likely to survive the fall to Earth.
"The smaller the debris is the more likely you are to get burn-through. So if you fragment something before re-entry, less mass will survive to hit the Earth," he told BBC News.
But Russia's defence ministry has effectively branded the US operation a cover for testing an anti-satellite weapon.
The Russian defence ministry argued that various countries' spacecraft had crashed to Earth in the past, with many using toxic fuel on board, but that this had never before merited "extraordinary measures".
A spokesman for the Chinese foreign ministry in Beijing, Liu Jianchao, said China was concerned about the "possible damage to security in outer space and to other countries".
"We demand that the US... swiftly brief the international community with necessary data and information in time, so that relevant countries can take preventative measures," he said.
Last year, China carried out a test using a ground-based ballistic missile to destroy a satellite in space, prompting international alarm and fears of a space arms race.
On Tuesday, a US State Department spokesman stressed that the action was meant to protect people from the hazardous fuel and was not a weapons test.
The US government has also denied claims that the main aim of the operation was to destroy secret components on USA 193.
Officials say classified parts would be burned up in the atmosphere and, in any case, that would not be a reason for shooting down the satellite.
1 SM-3 missile launched from a US Navy cruiser in Pacific Ocean
2 The three-stage missile headed for collision location, where the relative "closing" speed was expected to be 10km/s (22,000mph)
3 Satellite came in range at altitude of 247km (133 nautical miles), close to edge of Earth's atmosphere
4 Missile made contact with satellite with objective of breaking fuel tank, freeing hydrazine into space
5 Much of the debris will burn up but an as yet unknown amount is expected to be scattered over hundreds of kilometres