Opposition leader and former premier Ranil Wickremesinghe warned that the spread of diseases in the camps during the current rains could worsen conditions for nearly 300,000 civilians held in camps.
"Sri Lanka's image will be damaged further if the situation inside camps worsens during heavy rains," Wickremesinghe said. "The government will not be able to re-settle displaced people during monsoon showers.
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Sri Lanka is already facing condemnation from international rights organisations and aid agencies for its treatment of the civilians who were displaced during fighting that ended in May.
However, the government has promised to resettle 80 percent of some 300,000 ethnic minority Tamils who were displaced during the final stages of the war in the north by the end of this year.
Heavy showers over the weekend lashed the northern Vavuniya district where most of the displaced people are housed in makeshift camps.
The rains washed away flimsy plastic shelters and wooden floor toilets,