Sri Lanka, under heavy pressure to end human rights abuses four years after the end of a brutal civil war with Tamil Tiger rebels, has said it faced a new threat of "terrorism and Muslim extremism".

Groups linked to the Liberation of Tamil Tiger rebels had been trying to undermine government reconciliation and development efforts, Defence Secretary Gotabaya Rajapaksa, younger brother of President Mahinda Rajapaksa, said on Tuesday.

"These include winning of international opinion for the separatist cause... and pushing for the resumption of conflict through reorganising of local militant activities in Sri Lanka," Rajapaksa told a defence seminar.

Buddhist-majority Sri Lanka faced possible threats from groups involved in previous insurgencies, trying to mobilise people to once again take up extreme left-wing causes, Rajapaksa said. 

'More authoritarian'

The comments came three days after UN Rights Commissioner Navi Pillay said people were still suffering amid signs the country was becoming more authoritarian. 

More recently, there has been increasing violence against Muslims, mirroring events in Buddhist-majority Myanmar.

In March, the UN Human Rights Council passed a resolution calling on the Sri Lankan authorities to thoroughly investigate alleged war crimes committed by government troops and Tamil fighters.

The UN says it has "credible allegations" that Sri Lankan troops and rebels both carried out atrocities and war crimes and up to 40,000 civilians were killed in the final months of the war.

Source: Agencies