Mr Lee faces plummeting support, four months after taking office
South Korean President Lee Myung-bak has announced he is replacing several top aides, following public outcry over a beef import deal.
Mr Lee said the decision to replace his chief of staff and six senior secretaries was aimed at giving his administration a fresh start.
Support for the new government has nosedived over its decision to resume imports of US beef.
Protesters say the deal fails to protect them from mad cow disease.
US and South Korean officials are currently trying to come to an agreement
South Korea used to be a major market for US beef, but suspended imports in 2003 after a case of the disease was identified there.
The government's decision in April to lift the suspension sparked weeks of demonstrations. Scores of people have been arrested in occasionally violent clashes.
Mr Lee announced the high-level replacements in a televised address - his second in two days.
On Thursday he formally apologised to the public for failing to address their concerns on the beef issue.
The president said he had backed the beef deal to help secure passage of a bilateral free trade agreement that would boost the economy - but he added that he had acted "in a hurry".
In a bid to defuse public anger, South Korea has asked the US to agree not to export beef from cattle aged over 30 months - which are thought to carry a higher risk of mad cow disease.
Negotiators from the two sides have held a week of talks on the issue in the US capital Washington.
After a final meeting late on Thursday, they said they were close to a mutually-acceptable agreement.
The talks yielded "considerable progress", South Korea's foreign ministry said, and "both sides neared mutually satisfactory results".
The envoys will now report back to their respective governments for further consultations, the ministry said, before the details were made public.
The number of protesters on the streets of Seoul has begun to fall since Mr Lee's government said it would seek import limits.
But beef is not the only problem facing the president.
His administration is also facing strikes from long-haul lorry drivers, construction industry workers and members of the militant Korean Confederation of Trade Unions who oppose his plans for privatisation and pension reform.
Mr Lee could also face a backlash over worsening economic conditions.
When he took office, he vowed to bring economic growth - but instead the country is battling a global downturn and rising inflation.