By Park Tae-woo

President Lee Myung-bak strongly warned North Korea, in a very harsh tone that the communist state will pay a price corresponding to its acts.

He further elaborated that South Korea will no longer tolerate North Korean provocations and will change its military posture from passive defense to proactive deterrence.

It is very timely and proper for him to mention tough sanctions against North Korea. He sternly warned that if our territorial waters, airspace or land are militarily violated, we will immediately exercise our rights of self-defense.

From that moment of warning, no North Korean ship will be allowed to pass through any of the shipping lanes in the waters under our control, which had previously been allowed by the Inter-Korean Agreement on Maritime Transportation.

Following President's Lee's address, the foreign and unification ministers held a joint press conference detailing the government's military, economic and diplomatic actions to punish North Korea, including investment and exchange bans and military drills with U.S. forces focused on the reclusive nation.

The Ministry of Unification will be responsible for the measure to bar North Korean ships' passage through the South's waters; the Ministry of Foreign Affairs and Trade will bring the matter to the U.N. Security Council; and the Ministry of National Defense will actively participate in the Proliferation Security Initiative (PSI) drills in the international dimension.

After the international team of experts clearly concluded that a North Korean submarine infiltrated South Korean waters west of the peninsula and fired a torpedo at the Navy warship Cheonan, sinking it and killing 46 sailors on March 26, the U.S. strongly backed South Korea's stance by issuing a strong statement saying that Seoul's responses are entirely appropriate.

Even President Barak Obama supported South Korea by saying, ``The Republic of Korea can continue to count on the full support of the United States. U.S. support for South Korea's defense is unequivocal."

Obama has even directed his military commanders to coordinate closely with their Republic of Korea counterparts to ensure readiness and to deter future aggression.

Amid these kinds of swift and proper punitive moves, North Korea said that it would shoot at loudspeakers in the Demilitarized Zone (DMZ) if they are used to broadcast propaganda.

The threat was a direct response to the South Korean declaration that it would resume its psychological warfare against North Korea as a kind of countermeasure for the North's torpedo attack. This attitude of North Korea creates instability and causes security concerns among people in the South.

It is high time for North Korea to apologize for the Cheonan incident and promise never to inflict such misery in the future, showing sincerity.

North Korea lives in a different world of isolation and antagonism manipulated and operated by the dictatorial regime. The North should stop its infamous behavioral patterns by abandoning the false charge that the Cheonan incident was fabricated by the South.

At this moment, making North Korea openly admit to its provocation seems to have two unfortunate hurdles.

One is the negative attitude of some pro-North Korean groups in South Korea. Some intellectuals and politicians still create divisions on how to confront North Korea by spreading false rumors about the result of the international experts probe on the incident. They still do not give them full support to conclude that it was done by North Korea.

Some pro-North Korean politicians even criticize the government's sincere efforts to investigate the causes of the attack by saying that the ruling camp is trying to make a favorable local election ground to gain more votes by utilizing the naval incident.

With this kind of confrontation and schism between the ruling and opposition political groups in South Korea hanging on, it will never be effective to have a united front to tackle North Korea's ruthless and groundless propaganda.

It is in stark contrast to the U.S.'s united response against the terrorists attack after the 9/11 attack in New York City.

The other one is the vague attitude of Beijing on this matter, showing a continuing unconditional love toward North Korea. Without China's cooperative stance on this matter at the U.N. Security Council proceedings, a powerful resolution overwhelming Resolution s1718 and 1874 will not be adopted in the council.

China, as a responsible member of international community, must stick to the universal value of peace and stability on the Korean Peninsula.

It is our earnest hope for China to agree to the vivid and irrefutable fact that the joint investigation team of the civilian and military experts clearly proved that the sinking of the Cheonan was caused by a torpedo attack by North Korea, with the full verification materials and trustworthy process of scientific evidences to exclude any reasonable doubt.

We could no longer endure the blackmailing politics of North Korea, and some pro-North Korean groups' anti-South Korean activities that benefit the North.

It is, at this juncture, more than natural for South Korea to get tougher with the North, and also with some pro-North Korean groups within South Korea.

Some opposition politicians and activists should no longer argue that the government and the military are largely responsible for the tragedy.

They should know that, no matter what, their responsibility cannot be greater than that of the offender. What matters is they are not condemning North Korea at all.

China and some pro-North Korean politicians and activists in South Korea should stop those irrational arguments. Instead, they should stick to international norms and agreements.

Dr. Park Tae-woo is a visiting professor at the department of diplomacy at National Chengchi University in Taiwan. He has recently lectured on major international issues in prominent universities such as Korea University, Incheon University and Pai Chai University. He also serves as honorary consul of East Timor in Korea and secretary-general of the Democratic Pacific Union Korea Chapter. He can be reached at t517@naver.com.