Cambodia's decision to ask for Unesco status sparked tensions
Cambodia has again warned Thailand against crossing a disputed border, saying such a provocation could lead to "large-scale conflict".
Foreign Minister Hor Namhong accused Thai troops of trying to cross into Cambodia near an ancient temple, the scene of a recent military clash.
Both countries claim they own the area around the Preah Vihear temple.
Hor Namhong made the comments after talks with his Thai counterpart Sompong Amornviwat failed to reach a deal.
The standoff between the two countries centres on 1.8 square miles (4.6 sq km) of scrub near the 900-year-old Preah Vihear temple, which sits on a jungle-clad escarpment dividing the countries.
An international court awarded the temple to Cambodia in 1962, but land surrounding it remains the subject of rival territorial claims.
The decision by the UN in June to list Preah Vihear as a Unesco World Heritage Site reignited lingering nationalist tensions over the issue.
In early July Cambodian troops detained three Thai protesters who had entered the site illegally, sparking the military stand-off.
The two sides have already held several rounds of talks on the issue, but failed to reach agreement.