COLOMBO -- Security forces went on alert Sunday as Tamil residents called another work stoppage in eastern Sri Lanka to protest the killing of seven men by police, officials said.

The strike crippled transport in the eastern district of Batticaloa as well as parts of the neighboring Ampara district, where the police on Wednesday shot at mobs that tried to storm a commando base.

An earlier strike Friday called by members of the minority Tamil community turned violent, with three people killed in a grenade explosion, prompting authorities to clamp an overnight curfew in Trincomalee, AFP reported.

Officials said Interior Minister John Amaratunga was visiting Trincomalee Sunday and the situation appeared to be under control.

Army General Anton Wijendra had earlier gone to the area to restore order.

Wednesday's shooting was the worst bloodshed since the government and the rebel liberation Tigers of Tamil Eelam entered an indefinite cease-fire February 23, which has largely held despite mutual accusations of violations.

Scandinavians monitoring the truce in Sri Lanka called for restraint following the incident and said they had no evidence the Tiger leadership knew in advance about the storming of the police base.

The government and the tigers entered formal negotiations last month in Thailand under Norway's Aegis and are due to meet again in late October.

The talks are aimed at ending three decades of ethnic bloodshed that has left more than 60,000 people dead.