At least 21 people were killed in the southern Philippine province of Maguindanao on Monday, in what the authorities described as one of the country's worst cases of political violence in recent memory.

The deaths came three days after the start of the 12-day period for the filing of candidacies for national and local polls next May, and has put pressure on Gloria Macapagal Arroyo, Philippine president, to declare emergency rule in the province, which is 930km south of Manila, to prevent more bloodshed.

“This is a gruesome massacre unequalled in recent history,” said Jesus Dureza, Mrs Macapagal's adviser on the southern Philippines. He urged the president to declare a “state of emergency” in the area and bring in the military to disarm the groups involved. “Anything less will not work,” he said.