The deal has drawn tens of thousands in total to a series of candlelit protest rallies amid a growing scare over mad cow disease. Activists on Tuesday called for a new five-day vigil until Saturday in Seoul.

Opposition parties in parliament have said they will not ratify a sweeping free trade agreement with Washington unless the Seoul government agrees to renegotiate the beef deal.

Mr Lee's government has ruled out renegotiation and insists US beef is totally safe. But the new president said it had failed to make its case.

'I cannot but admit that the government somewhat failed in communicating with the people before and after (the deal),' he said at a cabinet meeting.

'I have come to learn how great people's concerns are about health and food safety.'

Opening the beef market is an essential US precondition for approval of the separate free trade pact. It was signed last June but legislators in both countries must ratify it.

On the eve of Mr Lee's first summit with President George W. Bush last month, Seoul agreed to lift its intermittent ban on US beef, which was imposed in 2003 over mad cow concerns.

Members of parliament's foreign affairs committee on Tuesday began a two-day hearing on the free trade pact and plan to question up to 30 government officials.

Mr Lee urged parliament to ratify the trade pact, which he said would be beneficial to the nation.

But three opposition parties dominate the outgoing parliament whose last sitting is late this month.

The next National Assembly will be controlled by Mr Lee's Grand National Party after it won an overall majority in the April 9 election. But the government wants the trade pact ratified this month, to put pressure on the US Congress also to act quickly before election concerns preoccupy Washington.

US Commerce Secretary Carlos Gutierrez will visit Seoul on Thursday and Friday to press for approval of the trade pact.

'The US-Korea Free Trade Agreement is the most economically significant agreement that the US has negotiated in years, and will allow our two nations to stay ahead of the curve in an increasingly competitive global economy,' he said in a statement. -- AFP