Bolivia ? President Evo Morales on Saturday accused an opposition governor of using foreign thugs against government supporters in violence that has claimed at least 18 lives and prompted him to declare martial law in a breakaway province.

In a bid to defuse the bitter dispute over a new constitution and land reform that threatens to tear apart the poor Andean nation, Chile called for an emergency meeting of South American leaders on Monday.

“A larger tragedy has to be avoided,” said Venezuelan President Hugo Chavez, a strong ally of Bolivia’s leftist president, confirming he would attend the meeting.

Morales described as an ambush a gunbattle in the eastern province of Pando on Thursday that led him to impose martial law the next day. “These people were massacred,” he told a news conference on Saturday.

Interior Minister Alfredo Rada said 16 people were killed in the clash – the majority of them peasants who back Morales – and authorities said another two people died Friday at Pando’s main airfield as government troops took control, opening fire to disperse protesters.