SEOUL, Korea, Republic Of -- North Korea has launched an estimated 1 million propaganda leaflets by balloon into South Korea amid increased tension between the rivals following the North's recent nuclear test, Seoul officials said Monday.

A Cold War-style standoff has flared since North Korea's claim on Jan. 6 that it tested a hydrogen bomb. South Korea resumed blasting anti-North propaganda broadcasts and K-pop songs from border loudspeakers. North Korea quickly responded by restarting its own border broadcasts and floating the balloons over the border carrying anti-South leaflets, according to Seoul officials.

Seoul's Defence Ministry said Monday the North's military has been sending the balloons on a near-daily basis. Spokesman Kim Min-seok said the leaflets have reached Seoul in addition to areas close to the border.

Such leafleting by the North is rare, as the two Koreas officially stopped psychological warfare as part of tension-reduction measures in 2004. South Korean activists have still occasionally sent propaganda balloons toward North Korea, triggering angry responses from the North.

South Korean officials believe their broadcasts will sting in the rigidly controlled, authoritarian country by demoralizing frontline troops and residents. There are doubts in Seoul that the North Korean leaflets will have any impact on the public in more affluent South Korea.

Leaflets discovered at a South Korean border town contained cartoon images showing South Korean President Park Geun-hye wearing a bikini and falling headfirst into a slop bucket. The leaflets referred to her as "human filth." It is not the first time North Korea has lashed out at Park, the South's first female president, in a sexist or derogatory manner. It has previously referred to her as a prostitute.

Many foreign governments and analysts remain highly skeptical about the H-bomb claim, but whatever the North detonated underground will likely push the country closer toward a fully functional nuclear arsenal, which it is still not thought to have. The North previously conducted atomic bomb tests in 2006, 2009 and 2013.

South Korea, the U.S. and other countries are pushing hard to get North Korea punished over the bomb test. Soon after the test, diplomats at a UN Security Council pledged to swiftly pursue new sanctions on the North. But it's unclear whether China, the North's last major ally and a veto-wielding permanent member of the Security Council, would co-operate on any tough sanctions that could force a change in the North.

The two Koreas share the world's most heavily fortified border since their war in the early 1950s ended with an armistice, not a peace treaty. About 28,500 American troops are deployed in South Korea as deterrence against North Korea.