Sri Lanka's army Sunday denied involvement in an armed robbery at the home of a journalist who has been critical of the government.

But it said two military deserters were among those involved in the crime.

Five men held the editor at knifepoint and searched her Colombo home in a pre-dawn raid Saturday after saying they wanted to steal jewellery and cash, but police burst in and shot dead one of the intruders.

The island's main press freedom organisation, the Free Media Movement, said it suspected the robbery was linked to the work of Sunday Leader associate editor Mandana Ismail Abeywickrema.

However, the army and the police insisted it was an attempted robbery.

"It is deplorable that some parties (are) trying to implicate the army in this criminal act carried out by a gang of robbers among whom two soldiers -- one deserter and another awaiting discharge from service -- were present," the army said in a statement.

It came as the UN human rights chief Navi Pillay began a week-long fact-finding mission to Sri Lanka.

Police have yet to disclose details of those arrested in connection with the incident.

The attack was the latest of several violent incidents involving the staff of the privately-run Sunday Leader.

Abeywickrema has been critical of the government in her political commentary and recently set up a trade union for journalists.

In 2009 the Sunday Leader's editor Lasantha Wickrematunge, a staunch critic of the government, was shot dead near his office just outside the capital.

Six months ago gunmen shot and wounded another of the paper's journalists at his home near Colombo.

The investigative newspaper was considered anti-government until last year, when it was bought by a businessman who is widely seen to favour President Mahinda Rajapakse's administration.

In September the newspaper's new owner dismissed the editor, Frederica Jansz, who said she was fired after resisting demands to water down criticism of the president.

She has since fled to Canada, saying she received death threats.

Media rights groups have said Sri Lanka remains a dangerous place for journalists despite the end of a decades-long war between the military and Tamil separatist rebels in 2009.

Sri Lanka lifted a state of emergency in 2011, but media activists say journalists have been forced to self-censor their work due to fear of attacks.