Myanmar leader General Than Shwe on Saturday warned his country to be alert against the West after his military junta was slammed for arresting pro-democracy leaders. "The old and new colonialists alike bent on occupying and holding sway over our union have hatched wicked schemes to weaken our national solidarity which is the foundation of our union," Shwe said.His message was read out at a ceremony to commemorate Union Day, which marks a key pre-independence event. It came after the United States and United Nations slammed the country's military junta for arresting several pro-democracy leaders and prohibiting groups from commemorating the day. Among those held was Hkun Htun Oo, the chairman of the Shan National League for Democracy, which won 1990 elections in a result the junta refused to acknowledge. "The United States is deeply concerned" about the arrest, US State Department spokesman Richard Boucher said on Friday. Boucher also expressed concern the military had prohibited the United Nationalities Alliance, Myanmar's leading coalition of pro-democracy ethnic political parties, from commemorating Union Day.