By Alex Jensen

SEOUL

This week marks the arrival of spring according to Korea's traditional lunar calendar, but there was no sign of a North-South thaw Monday as Seoul insisted it would be suspending all civilian exchanges.

South Korea's move follows the North's claimed hydrogen bomb test last month.

"The Korean Peninsula faces a very grave situation due to the North's nuclear test, so the government thinks that this is the time for a temporary suspension," Unification Ministry spokesperson Jeong Joon-hee told reporters.

Inter-Korean civilian exchanges surged late last year on the back of a landmark Aug. 25 cooperation agreement between Seoul and Pyongyang.

Citizens from both sides require permission to visit each other's countries, which remain in an uneasy state of truce as a peace treaty was never signed after the 1950-53 Korean War.

According to government data, 880 South Koreans traveled to the North in October -- more than double the figure for the entire period between January and September.

That did not even account for visitors to the joint Kaesong Industrial Complex or the hundreds involved in family reunions, which were another key outcome of the August breakthrough.

While there has been no suggestion that the Kaesong facility will shut down as it did amid tensions in 2013, the present suspension of civilian exchanges will put on hold plans for cultural and sporting encounters.

Notable projects last year included the provision of aid to the impoverished North, excavation work at the site of an ancient palace and football friendly matches between labor union members.

But the spirit of promoting unity on the peninsula changed entirely last month after Pyongyang ignored a series of United Nations resolutions by conducting its fourth ever nuclear test.

With that test yet to be punished by the UN Security Council, local news agency Yonhap reported Jeong as suggesting that Seoul was suspicious of any moves by North Korea to downplay the seriousness of its provocation.