North Korea finished installing the last and third stage of the long-range rocket on the launch pad Wednesday and could launch it as early as Monday, a Seoul government source said.

The fuel injection process is expected to begin this weekend after a technical inspection of the rocket, assembled at the Dongchang-ri launch site in North Pyongan Province, the source explained, declining to be named.

The rocket should be launched within one to three days after the fueling given that oxidation agents, if left unused for long, would corrode the interior of the delivery vehicle and undermine its propulsion.

“We judge that the North has completed the work of erecting all the stages. Some of the workers have left the assembly site (as their work was over),” said the source.

“If the fueling process begins, we should detect the arrival of fuel containers around the site (through analysis of satellite imagery).”

But he added that as the fuel injection facility is located underground, there are some movements that cannot be detected by satellite.

Analyzing images provided by the U.S. firm Geoeye Satellite Image, the Washington-based Radio Free Asia said Pyongyang may launch the rocket in the early part of the Dec. 10-22 period, during which the North said it would fire the rocket.

Seoul’s state weather agency forecast no rain or snow around the launch site between Monday and Wednesday. But it would be cloudy during the period. Experts say the rocket can be fired should there be no lightning.

A local expert told media that the rocket may travel a distance of some 10,000 kilometers if it is the same rocket used in the North’s April launch.

“The ‘burn-out’ time for the first-stage engine of the Unha-3 rocket was 130 seconds. This allows us to estimate that the range could be around 10,000 kilometers,” said the expert.

Amid the reclusive state’s push for the launch, Seoul, Washington and Japan have been stepping up their cooperation in urging the North to stop the provocative move. All three believe the satellite launch is a disguised missile test.

Seoul’s chief nuclear envoy Lim Sung-nam, his U.S. counterpart Glyn Davies and Shinsuke Sugiyama, Tokyo’s point man on North Korea, held a brief meeting to discuss the pending issue in Washington on Tuesday.

Before the talks, Lim, Davies and other U.S. State Department officials held a separate meeting on the issue. Since last week, the allies have consulted on the scope and content of additional sanctions against Pyongyang.

“Seoul and Washington have agreed to maximize diplomatic efforts to deter the North from going ahead with the launch,” Lim told reporters.

“We also concurred that should the North’s plan be into practice, the U.N. Security Council should take necessary action in line with its presidential statement (issued in response to the North’s failed rocket launch in April).”

He also said that the allies would step up diplomacy to make China and Russia join their efforts to block Pyongyang’s rocket launch.

As media focus on additional sanctions against the North, Lim stressed that Seoul and Washington, for now, prioritize preventing the launch rather than focusing on punitive measures.

“It is not appropriate to discuss details (of anti-Pyongyang punishments) yet,” he said.

U.S. Secretary of State Hillary Clinton on Tuesday expressed deep concern about North Korea’s launch plan during a meeting of the NATO-Russia council.

“The U.S. is deeply concerned about North Korea’s recent announcement that it plans to carry out another rocket launch,” she said. “We urge everyone here to publicly call upon North Korea to comply fully with its U.N. Security Council obligations.”

South Korea and the U.S. are reportedly considering a set of stronger sanctions against the North. They include financial sanctions and an expanded ban on maritime shipments of North Korea’s military exports.

Meanwhile, South Korea’s military is to deploy the ground-based Israeli-made Green Pine early warning radar system with a detection range of 500 km to better deal with North Korea’s missile threat. The radar system is to play a core role in the Korea’s low-tier missile defense program.

“The overall process to test the radar, brought into Korea in August, ends on Wednesday. This should be operable when the North launches the long-range rocket,” said a military source on condition of anonymity.

By Song Sang-ho (sshluck@heraldcorp.com)