YANGON (AFP) - UN Secretary-General Ban Ki-moon has called for a "serious effort" to end the conflict raging in northern Myanmar, where ethnic minority Kachin rebels accused the military of breaking its ceasefire. PM Thein Sein's reformist govt announced on Friday that it was ending a military offensive against the Kachin rebels, but fresh fighting erupted over the weekend. Ban "calls upon both sides to make serious effort to create conditions for sustained peace in Kachin through enhanced confidence building measures and political dialogue", the UN said in a statement released in New York on Sunday. About a dozen peace activists meanwhile set off Monday on a planned 1,300-kms  walk from Yangon to the rebel stronghold of Laiza to call for an end to the conflict.