Ethnic rebels killed 20 Myanmar troops in an ambush aimed at deterring the military government from launching an offensive against them ahead of elections this year, a rebel spokesman said Friday. The incident took place on March 13 in Nam Zam township of Shan State, a remote region bordering Thailand and China under control of armed ethnic Chinese groups for decades. Troops were ambushed by rebels from the southern wing of the Shan State Army (SSA), spokesman Sao Lao Seng said by telephone. The firefight lasted about three hours and no rebel troops were killed, he said, adding it was the third such clash this year. “The ambush was planned after the regime has been threatening to launch offensives against us,” he said. Eight soldiers were wounded. The report could not be immediately verified. Myanmar's state newspapers, mouthpieces for the media-shy junta, have made no mention of the incident. Activists and ethnic groups say tens of thousands of troops have been mobilised in the mountainous region ahead of an impending offensive to flush out rebel armies resisting demands to disarm, transfer their fighters to a state-run Border Guard Force and join the political process. But most groups, which have a deep distrust of Yangon and have enjoyed de facto independence for decades, have refused the junta's “offer”, saying they have nothing to gain from polls. Analysts say Myanmar's government wants all groups to take part in elections, the first in two decades, to show the country is fully behind the political process. The election, a date for which has not yet been set, has been widely derided as a sham to entrench the army's rule over the resource-rich Southeast Asian nation. The cooperation of ethnic groups would allow the junta to take control of the rebellious region for the first time since it took power in 1962. Generals from the regime have repeatedly held talks with leaders of the ethnic groups, six of which have agreed to disarm. However, it is unlikely the bigger armies will follow suit. “The negotiation process appears to be over. Both sides have refused each others' proposals,” said an official in the SSA's political wing, who asked not to be identified because he is not permitted to speak to the media.