North Korea's official media responded to Friday's launch by threatening that Japan would "be held fully responsible for causing a new arms race" in north-east Asia".
The rocket carrying the satellites took off at 1027 on Friday (0127 GMT) from the remote island of Tanegashima, 1,200 kilometres (700 miles) south-west of Tokyo.
It marked the start of an intelligence-gathering programme prompted partly by North Korea's launching of a long-range ballistic missile over Japan in 1998, although Pyongyang said it was a rocket launching a satellite.
The North Korean KCNA news agency warned on Friday that Tokyo was "wantonly violating" an agreement on improving relations made by Japanese Prime Minister Junichiro Koizumi and North Korean leader Kim Jong-il last year.
At that summit, North Korea pledged to extend its moratorium on ballistic missiles beyond 2003.
Japanese intelligence has indicated in recent weeks that Pyongyang was planning to fire off another ballistic missile.
Officials said on Friday there was no sign such a test was imminent.
Lift-off
The two satellites, the first of at least four in the 250-billion-yen ($2.05bn) spy programme, were propelled into clear but windy skies by a Japanese-made H2-A rocket.
They are intended to give Tokyo independent surveillance capabilities, since it has used US-gathered intelligence until now.
Japan is thought to be especially concerned about North Korea's Taepodong missiles, which are able to reach virtually all of the country. It also wants to monitor Pyongyang's nuclear weapons programme.
Japanese officials have stressed that the satellites, which will orbit the Earth at a height of 400 km to 600 km (250 to 370 miles), can also be used for monitoring weather, crop conditions or natural disasters.
They will not be fully operational for several months.
Cabinet Secretary Yasuo Fukuda said they were not intended to provoke North Korea.
But a Japanese military analyst, Hajime Ozu, told the Associated Press that it was likely Pyongyang would respond.
"For North Korea, a missile launch means a way to boost patriotism at home and a warning to the United States... It is one of the few remaining key diplomatic tactics North Korea has," he said.
Military shift?
Rising tensions with North Korea over its nuclear weapons programme have underscored Japan's vulnerability.
On Thursday, Japanese Defence Minister Shigeru Ishiba said that Tokyo would consider developing offensive capabilities, something that would go against Japan's pacifist constitution.
But on Friday, Prime Minister Junichiro Koizumi denied that was a possibility.
"I am aware that there has been talk about the question of acquiring offensive weaponry capable of striking an enemy whose intent to attack is clear, but this government has no such intention," he told lawmakers.
Mr Ishiba also told the South Korean paper, Chungang Ilbo, that Japan would not respond to North Korea's threats by joining it in a nuclear arms race.
He said that as the victim of nuclear attacks in 1945, "we are not even thinking about having nuclear weapons".
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