"The Commonwealth will rightly face international ridicule if it goes ahead with its summit in Sri Lanka," said Brad Adams, Asia director at Human Rights Watch.
The Commonwealth Ministerial Action Group (CMAG), a grouping of Commonwealth leaders that addresses "serious or persistent violations" of the Commonwealth's fundamental political values will tomorrow meet in London.
"The CMAG meeting should send a message to the Sri Lankan government that the scale and severity of its abuses violate the Commonwealth's core values and will not be rewarded," Adams said.
The HRW said Sri Lanka has taken no meaningful steps to address serious abuses by government forces in the last stages of the conflict against the LTTE in 2009.
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Since 2009, Sri Lankan government has been responsible for a worsening human rights situation that includes clampdowns on basic freedoms, threats and attacks against civil society and actions against the judiciary and other institutions imperilling Sri Lankas democracy, it said.
"To allow Sri Lanka to host the summit without rapid improvements would be to reward an abusive government with an undeserved badge of international acceptance," he added.
Sri Lanka dismisses all accusations as politically motivated, unfounded and directed by the pro-LTTE diaspora in the West.