US President Barack Obama urged China on Sunday to exert more pressure on the Democratic People's Republic of Korea (DPRK) to resolve the Cheonan issue. The Cheonan was a corvette of the Republic of Korea (ROK) that sank on March 26, 2010.

This ploy of the US is not new. Actually, some US scholars had been repeatedly saying that China was the key factor in dealing with the DPRK. In their articles, using the Cheonan incident as an example, William H. Tobey, senior fellow at Harvard Kennedy School's Belfer Center for Science and International Affairs, and Will Marshall, president of the Progressive Policy Institute, have argued that China has "coddled and appeased the DPRK" and it is crucial to handling the Korean Peninsula issue.

The fact remains that no conclusive evidence has been found to implicate the DPRK in the Cheonan incident. An explosion near the Cheonan caused it to break in half and sink. After the remains of the ship were hauled up, an international investigation team was formed to determine the cause of the sinking. On May 20, the multinational panel concluded that the cause was a "non-contact underwater explosion triggered by a torpedo that was fired by a midget submarine of the DPRK".

But the torpedo fragments and the traces discovered by the ROK are not conclusive evidence. How could a torpedo that blasted a warship survive with its screw shaft and engine intact?

The Cheonan incident, at best, is the continuation of the dispute over territorial waters between the DPRK and the ROK. Because of the heavy casualties and furious public sentiment, the ROK is facing unprecedented pressure to do something. Targeting the DPRK - and making China a key factor in the political game - is the ROK's most realistic choice for diverting public attention.

Washington's stance over the incident has changed from initially downplaying suggestions of Pyongyang's involvement to later categorically accusing it of sinking the ship.

Let's look at the timing of the Cheonan incident. It took place when the Greek debt crisis had spiraled out of control and the euro had dropped sharply. The DPRK-ROK crisis shifted the focus from China-EU cooperation, too.