Israel has refused to allow international monitors or peacekeepers into the country.
The liberation army has agreed to allow 150 foreign and Colombian monitors into the zone to investigate villagers' complaints.
But Mr. Milosevic, who had offered to allow international monitors, withdrew the offer.
When the government ceded land to Colombia's largest rebel group in 1998 as a peace gesture, the rebels declined to allow international monitors into the area.
He withdrew his offer to allow international monitors to check on the passage of goods across the border.
The new deadline, which is to sign a deal allowing monitors into the country, will be the end of today, 00.00 GMT.
Algeria allowed foreign electoral monitors for the election.
President Milosevic of Serbia has withdrawn an offer to allow international monitors along the border because he no longer fears American military intervention.
Both sides agree to allow Indonesian monitors to prevent further clashes.
The design might also allow large monitors to be hung from a wall.