Japanese media, citing unnamed government sources, report that citizens of the country were advised to raise the national flag at 0700 Prague time and watch a message on television.
But that time passed without word of any launch.
Reports say the order may have just been part of preparations for the marking of the 42nd anniversary of North Korean leader Kim Jong Il taking a role in the Communist Party.
But Japanese officials say the communist regime could be preparing to fire a Taepodong-2 missile, which has a range of 3,500 to 6,000 kilometers.
U.S. State Department spokesman Sean McCormack said on June 16 that Washington would view a missile launch as a provocative act.
"We would regard a missile launch by North Korea as inconsistent with the September 19 six-party talks' joint statement that referred to joint efforts for lasting peace and stability in Northeast Asia. We would urge North Korea not to undertake such a provocation and instead, return to the six-party talks to achieve the vision laid out by the September 19 statement," McCormack said.
The United States had been involved with China, Russia, Japan, and South Korea in talks with North Korea to disband the reclusive state's nuclear arms program in return for security and diplomatic guarantees and energy aid.
The six-party talks came to a head in September 2005, with Pyongyang agreeing in principle to end its nuclear-weapons program.
But talks later collapsed after the United States imposed financial sanctions on North Korea for alleged U.S. dollar counterfeiting and money-laundering activities.
Japanese Foreign Minister Taro Aso said today his country would seek an immediate meeting of the UN Security Council if Pyongyang went ahead with the intercontinental ballistic missile test.
The foreign minister voiced concern about the possibility of a missile dropping accidentally on Japan.
Aso stopped short of saying what Japan and the United States would do in the event of a launch, but said the responses would be "rather harsh."
Meanwhile, the United States promised to protect itself. "We have a variety of national technical means that we could use to monitor the situation," State Department spokesman McCormack said. "We, of course, will take necessary preparatory steps to track any potential activities and to protect ourselves."
Pyongyang stunned Tokyo and other nations when it test-fired a Taepodong-1 missile with a range of up to 2,000 kilometers over Japan in 1998. It claimed then it was seeking to place a satellite in orbit.
In 2002 it agreed not to test long-range missiles in a declaration with Japan paving the way for the normalization of relations.