South Korean activists have floated leaflets attached to balloons into North Korea, calling for the overthrow of North Korean leader Kim Jong-IL.

The activists, from a North Korean defector group, say they launched 10 gas-filled balloons carrying 200,000 leaflets from a mountain in a suburb west of Seoul.

The group, known as Fighters for Free North Korea, conducted a similar launch in March, with balloons carrying U.S. currency and messages critical of North Korea’s isolationist regime.

Pyongyang has threatened several times to fire on balloon launch sites, prompting group members to vow to persevere with their activism.

Cross-border tensions remain high on Thursday — one day after North and South Korea exchanged artillery fire along a flashpoint maritime border in the Yellow Sea. No casualties were reported in Wednesday’s exchanges.