UNITED NATIONS (CNN) -- The United Nations on Thursday announced that a treaty banning non-detectable, plastic land mines has been ratified by enough countries and will go into effect December 3.

The treaty is an early appendix, or protocol, to the overall ban on land mines, which has been signed by over 100 countries since a conference in Ottawa last year.

The International Campaign to Ban Landmines and its former leader Jody Williams won the Nobel Peace Prize in 1997 for their work in bringing world attention to the issue and were an essential part of bringing about the Ottawa conference.

Twenty-one countries, one more than needed, have ratified the protocol to date, a U.N. spokesman said.

The accord bans the non-detectable, plastic mines that can kill and injure decades after the end of a conflict and introduces technical rules to limit the lifespan of anti-personnel mines planted outside marked fields to three months. But it gives signatories nine years to switch to the detectable, self-destructive variety.

The ban also expanded the scope of an earlier weapons treaty to domestic and international conflicts. It imposes new export restrictions -- including an immediate ban on transfer of non-detectable mines.

U.N. officials said the overall land mine ban, known as the Ottawa Convention, had been ratified by 23 of the required 40 governments and predicted it would go into effect in the first quarter of next year.

The grim reality of land mine use was in full view Wednesday when members of a Peruvian military patrol stepped on land mines along a disputed stretch of the northern border with Ecuador, injuring five soldiers.

The soldiers were on a routine patrol in the mountainous Cordillera del Condor region, where the two countries fought a brief undeclared war in early 1995, when they stepped on the mines, a Peruvian Defense Ministry statement said. One soldier lost a leg in an explosion.

Peru charged that the mines were planted by Ecuadorean troops in Peruvian territory and will file a protest with an international peace mission monitoring the disputed region.