South Korea opened its border on Thursday to US beef from cattle under the age of 30 months.

It followed a deal to allow all US beef regardless of age into South Korea that was made in April, however huge protests and rallies in Korea pressured the government to suspend that agreement which was to have gone into effect on May 15.

Last week the two countries came to an understanding that the US would only ship beef from cattle less than 30 months old.

"We are charged at USDA to come up with a verification system and we will do so," US Secretary of Agriculture Ed Schafer says.

"We are just getting that requirement for USDA on the table and aren't exactly sure how we are going to implement it yet."

Mr Schafer told reporters Wednesday that for the time being methods such as oral examination of teeth will be used to determine age.

He says the number of premise registrations under the National Animal Identification System is not sufficient to meet export needs.

Despite the concessions, there is still widespread anger in Korea against the resumption of the US beef trade, with a mass of protesters, often violent, hitting the streets in Korea to coincide with the arrival of US Secretary of State, Condaleeza Rice.