SEOUL - SOUTH Korean police promised on Monday to crack down on protesters who block main streets as President Lee Myung Bak said the rallies against US beef imports are hurting the country's economy and image.

Seoul police said they would apply stricter rules to the mass candlelit vigils, which have lasted more than two months and occasionally ended violently.

The protests have sparked a huge deployment of riot police, baffling or alarming foreign visitors. They have also caused huge disruption in the heart of Seoul and hit city centre businesses hard.

On Sunday night officers sealed off City Hall plaza where some 500 people rallied, preventing them from marching on along main streets.

The demonstrations were sparked by Seoul's agreement in April to resume US beef imports, which were halted in 2003 after a US mad cow disease case.

Seoul went back to Washington to secure extra health safeguards before officially resuming the imports on June 26.

But some 50,000 people by police estimates still gathered peacefully Saturday in Seoul to demand the scrapping of the imports and Lee's resignation.

Mr Lee, in a BBC interview aired on Monday, admitted failings by his government.

Yonhap news agency said he would replace three of his ministers later on Monday.

'The government should have been more mindful and keenly aware of how high the people's expectations are when it comes to food safety,' he said.

Mr Lee acknowledged many were concerned about food safety. 'But at the same time there is a minority who for political or other reasons oppose the resumption of US beef imports.' He called for an end to the rallies and a focus on reviving the economy.

'If the demonstrations continue, I do believe it will have a very detrimental effect on the future of the Korean economy.

'It will also have a negative effect on how foreign investors perceive the future of the Korean economy as well as foreign governments dealing with Korea. They will have difficulty trying to understand why this is persisting.'

Religious groups, which recently joined the rallies, have decided to suspend activities.

'Following a meaningful declaration of the people's victory Saturday, the priests stopped fasting and returned to religious duty,' the Catholic Priests' Association for Justice said in a statement.

Buddhists called off a planned outdoor service in sympathy with the street protests that had been due Tuesday.

A group of Protestants that had organised outdoor prayer meetings in the past week said they would discontinue them.