Tensions are rising as the political talks stall
Their car was found at the bottom of the ravine on Friday, a day after contact with them was lost.
"The vehicle was blown up by a mine," said Norwegian Foreign Ministry spokesman Bjorn Berge. "We are reasonably certain that this was a powerful mine explosion."
There is no suggestion so far that the incident was the result of deliberate action by either of the two sides in the six-month conflict between ethnic Albanian guerrillas and security forces.
Deadlock
Macedonian Defence Ministry spokesman Marjan Djurovski said: "According to our information, the observer team was supposed to have been carrying out a mission in the area of Mazdraca and Novo Selo.
"A loud explosion was heard in this zone on Thursday, after which all contact with them was lost," he said.
The European Union has taken a prominent role in negotiations to find a political settlement in Macedonia but talks have stalled in recent days.
Negotiations were set to continue on Friday despite threats by the ethnic Albanian representatives to walk out.
The talks have become deadlocked over proposals by Western envoys to raise the status of the Albanian language - a plan criticised by the Macedonian prime minister.
Efforts thwarted
The BBC correspondent in Skopje says the two international mediators, Francois Leotard and James Pardew, appear to have managed to convince the Macedonian President, Boris Trajkovski, that their efforts will not jeopardize the territorial integrity of Macedonia.
Prime Minister Lubco Georgievski poured scorn on the mediators earlier this week, accusing them of siding with the Albanians.
Conscious that international efforts are being thwarted, the EU's foreign policy chief, Javier Solana and Nato Secretary-General Lord Robertson, have issued a statement calling Mr Georgievski's comments undignified and rejecting the idea that the international community is siding with anyone.
A slight increase in the number of minor violations of the ceasefire, brokered by Nato two weeks ago suggests that the guns cannot remain silent forever.