South Korea has been placed on high alert after neigbouring North Korea conducted an alleged hydrogen bomb test. Japan, on the other hand, has seemingly deployed a military aircraft to check for any radiation subsequent to the detonation.

Seoul military has stepped up surveillance over escalating tensions in the Korean peninsula. "Currently, our military is strengthening our vigilance and surveillance posture against North Korea," the country's defence ministry said in a statement.

South Korean President Park Geun-hye, who is heading a top-level security council meeting, has vowed that Seoul would retaliate strongly if provoked. She added that South Korea must make its northern rival pay the price for the nuclear test.

North Korea's adversaries including the US, Japan, and South Korea have already confirmed they will work together to draft a fitting punishment for North Korea. "Now, the government should closely cooperate with the international community to make sure that North Korea pays the corresponding price for the nuclear test," said Park.

"The test is not only a grave provocation to our national security but also a threat to our future ... and a strong challenge to international peace and stability," she added. The UN Security Council is also set to meet shortly to discuss measures against North Korea.

Meanwhile, Japan dispatched the military aircraft to check for radiation in aftermath of the alleged nuclear detonation, according to Kyodo news. So far, there has been no independent confirmation to assert North Korea's claims that it carried out a hydrogen bomb test.

Monitoring agency CTBTO has confirmed there was an "unusual seismic event" in the Korean peninsula and added that experts were investigating the incident. The agency said: "Our experts are now analysing the event to establish more about its nature."

Hydrogen bombs, unlike atomic bombs, are complicated to develop. Experts have so far remained sceptical whether the impoverished nation has the ability to come up with such sophisticated thermonuclear weapons. South Korean spy agency has already cast doubts whether the latest detonation was a result of hydrogen bomb.