June 25 (Reuters) - Myanmar security forces seized a large cache of weapons on a truck bound for Mandalay this week, after arresting insurgents following a firefight in the second-biggest city, state media reported on Friday. Since its Feb. 1 coup against Aung San Suu Kyi"s elected government, the military has tried to stamp out dissent and has killed or arrested hundreds of protesters. The junta"s opponents have formed militias known as People"s Defence Forces (PDF), most of which are lightly armed and have received limited training, with their attacks focused mainly in rural areas or smaller cities. The state-run Global New Light of Myanmar newspaper carried a photograph of four arrested people in front of a weapons cache. It said more than 100 firearms, 10,000 bullets, 499 grenades, plus bombs and detonators were seized. The report said those arrested confessed to receiving training and arms from the Kachin Independence Army (KIA), an ethnic minority army with a long history of conflict with the military. The newspaper said security forces made the arrests after a clash with the newly formed Mandalay PDF on Tuesday in which it said eight militia were killed and eight detained. Spokespersons for the Mandalay PDF and the KIA did not immediately answer calls seeking comment. At least 877 people have been killed by security forces and more than 6,000 arrested since the coup, according to activists" figures. The junta disputes those figures and says the number killed is much lower. In an interview with media in Russia during a visit this week, junta leader Min Aung Hlaing said the bloodshed was a result of protests going too far. "If it goes beyond the normal protests and leads to violence, the respective security forces will have to respond to avoid affecting the public and rule of law," he said, according to excerpts shared on the Telegram messaging app of military-owned Myawaddy TV. Min Aung Hlaing, who wore a business suit during the interview, said Myanmar needed stability and could start the process towards holding another election "roughly within two years". Most western countries have called not for an election but the reinstatement of the government of Suu Kyi, who is on trial accused by the junta of corruption and incitement, among other offences, which her legal team rejects. Efforts by Myanmar"s Southeast Asian neighbours to convince the junta to end violence and start dialogue with its opponents have so far been unsuccessful. Min Aung Hlaing stressed in the interview that Myanmar had no enemies but only friends, including the United States, and said Russia was "a very close friend".