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South Koreans called President Lee Myung-bak "The Bulldozer" when he plowed into office nearly three years ago with vows to stop coddling North Korea with unconditional aid.

These days, however, the nickname has started to ring hollow.

It originally denoted toughness and resolve, stemming from Lee's days as an aggressive construction CEO. But North Korea's brazen artillery attack on a South Korean island last week and a response slammed as weak are raising questions about Lee's readiness — and even willingness — to stand up to the North.

In the face of criticism, Lee replaced his defense minister and moved to boost troops on front-line islands. He has also promised tough consequences for any future aggression and expressed his outrage over the "ruthlessness of the North Korean regime."

He has issued similar pledges before, and the North Korean shelling on Nov. 23 that killed four South Koreans and destroyed parts of Yeonpyeong Island has prompted questions over what critics say is a failed policy toward the North.

The Dong-a Ilbo newspaper said in an editorial that after Seoul blamed North Korea for sinking a South Korean warship in March, Lee "promised a 'manifold retaliation' in the event of another provocation and a strike on North Korea's missile base if necessary."

"But his warnings have proven hollow," the newspaper said. "Many wonder if President Lee was resolute in deciding on retaliation" for the island attack.

The government faced more headaches Thursday, when opposition lawmakers expressed outrage over South Korean spy chief Won Sei-hoon's surprise acknowledgment of an intelligence breakdown.

Won told lawmakers in a private briefing that the South had intercepted North Korean military communications in August that indicated Pyongyang was preparing to attack Yeonpyeong and other front-line islands. Won didn't expect that attack to be on civilian areas and considered it a "routine threat," according to the office of lawmaker Choi Jae-sung, who attended the closed session.

South Korea's main opposition Liberal Democratic Party said the government had failed to deal with the North's artillery barrage, even though it had intelligence on an impending attack.

"Our intelligence system didn't work," Jun Byung-hun, the party's chief policymaker, said in a statement.

The National Intelligence Service on Thursday declined to comment.

Lee, who turns 69 this month, has been criticized for leading a military whose response to the Yeonpyeong attack was seen as too slow and too weak: the North fired 170 rounds compared with 80 returned by South Korea.

Satellite photos showed only about 10 South Korean rounds landed near North Korea's army barracks along the west coast, according to the office of lawmaker Kwon Young-se, who said he saw the images provided Thursday by the National Intelligence Service.

There is also disappointment with the South's perceived lack of preparedness despite warnings the North might stir up trouble amid an internal power transfer from Kim Jong Il to his son.

"After all the skirmishes and provocations, the country should have had a contingency plan — a rudimentary strategy of supplementing military power with naval and air forces" in the front-line island area, Song Ho-keun, a professor at Seoul National University, wrote in the JoongAng Ilbo newspaper.

To ease tensions, China, which is North Korea's only major ally, has pressed for an emergency meeting of the six nations who previously negotiated over Pyongyang's nuclear program: the two Koreas, China, Russia, Japan and the United States.

After walking away from the six-nation talks in April 2009, North Korea has shown it is eager to restart them to gain much-needed fuel oil and aid in exchange for nuclear disarmament. But Washington, Tokyo and Seoul are wary of talking with the North, and their top diplomats planned to meet in Washington on Monday to plot a strategy on dealing with the country.

Although it won't be part of that meeting, China said Thursday it would keep a "close watch" on the talks and sounded upbeat about what they could achieve.

"As the situation on the Korean Peninsula is highly complicated and sensitive, we expect the meeting to ease tensions and promote dialogue, rather than heighten tensions and intensify confrontation," Chinese Foreign Ministry spokesperson Jiang Yu said in a statement.

She said she also hoped the three countries would give "positive consideration" to China's proposal for emergency consultations among the participants in the six-party talks. Earlier Thursday, Jiang said that Russia had expressed interest.

On resumption of the nuclear negotiations, Seoul says North Korea must show real commitment to disarm. It has noted Pyongyang has gone in the wrong direction with its revelation last month of a new uranium enrichment facility that would give it a second way to make nuclear bombs.

During Lee's administration, Kim Jong Il has boosted his nuclear and missile capabilities, stoked military tensions and threatened to sever economic ties, oblivious to the South Korean leader's vows to get tough.

When the conservative former Seoul mayor came to power in February 2008, he rode a wave of frustration with the policies of his predecessor, the late Roh Moo-hyun.

Voters wanted Lee to use skills honed as a CEO to boost the economy, which many believed was mismanaged under the previous administration. Some, especially conservatives, were also critical of what they considered as support by the two previous liberal governments for Pyongyang and pursuit of high-profile joint industrial and tour projects without demanding concessions, such as progress on the nuclear issue, in return.

That "sunshine policy" was meant to encourage the North to become less antagonistic as economic, cultural and political relations warmed.

In sharp contrast, Lee linked economic aid to Pyongyang living up to its international commitments to abandon its nuclear weapons programs. Under his administration, criticism of the North became more vocal.

His stance enraged the country, which branded Lee a "traitor" and "human scum."

The shelling of tiny Yeonpyeong Island followed the March sinking of the South Korean warship that killed 46 sailors. An international investigation led by Seoul blamed a North Korean torpedo for the disaster, although Pyongyang denied involvement.

Besides dumping his defense minister after the island attack, Lee announced plans for new rules of engagement that call for stronger and more immediate military responses to aggression.

But Lee, now more than halfway through a single five-year term, must balance calls for a tough response with the knowledge that Seoul — a city of more than 10 million people and the economic heart of the country — lies within easy range of North Korean artillery.

Daniel Pinkston, Seoul-based analyst for the International Crisis Group think tank, said Lee also faces restraints that North Korea does not. He is leader of a robust democracy with an open economy that is vulnerable to the type of threats and tactics used by Pyongyang.

The crux of the problem, however, is that, despite "The Bulldozer's" tough words, South Korea's national security policy and defense readiness have weakened under his watch, he said.

"You have to be prepared," Pinkston said. "You can't be afraid to respond or go to war if you have to go to war."

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Associated Press writers Hyung-jin Kim in Seoul and Tini Tran in Beijing contributed to this report.