By C. Bryson Hull

COLOMBO, Jan 9 (Reuters) - Anger over the assassination of an outspoken Sri Lankan newspaper editor grew on Friday with the opposition forcing parliament to close early and hundreds of protesters demonstrating in the capital.

The killing of Sunday Leader chief editor Lasantha Wickramatunga on Thursday prompted diplomats on the Indian Ocean island to express concern to the Foreign Ministry and sparked condemnation from rights groups and even the World Bank.

In parliament, members of the main opposition United National Party shouted protests and waved placards, forcing the legislature to close.

Later, hundreds of journalists joined politicians and others in a major Colombo traffic roundabout, shouting slogans and waving placards saying "Stop Terrorism Against Journalists".

At least one gunman on a motorcycle intercepted Wickramatunga in rush-hour traffic, smashed the window of his vehicle with a steel bar and fired bullets into his head and chest. He died hours later.

President Mahinda Rajapaksa has ordered an investigation into Wickramatunga's killing.

In a televised address on Friday, he said the attacks had been carried out "to tarnish the image of the country internationally" and "and make room for various international forces to interfere to grab our gains away from us."

Wickramatunga's killing came two days after gunmen destroyed the main studios of Sri Lanka's largest independent and private broadcaster, which clashed with the government over its coverage of the war with the Tiger separatists and suicide bombings.

The Sunday Leader has been locked in court battles with many politicians over allegations of corruption.

"INTERNATIONAL CONSPIRACY"

The president said the government had a duty to expose those responsible.

"There is a conspiracy with certain international forces to achieve this sinister objective," he said, without naming those he thought were behind the conspiracy.

"We are aware that such conspiracies arise when a country moves ahead without giving in to external pressures."

The United States, the European Union, Canada and India all condemned the attack and demanded a swift probe.

Press watchdogs say Sri Lankan investigations into media killings have rarely, if ever, brought anyone to justice.

The World Bank in Sri Lanka issued a statement urging a transparent investigation and expressing "grave concern" over the attacks this week.

"Free and independent media is fundamental to the sustainable economic development of Sri Lanka," it said.

Journalists face murder, harassment, abduction and arbitrary detention in Sri Lanka, which press freedom groups count among the world's most dangerous countries for reporters.

The Asian Human Rights Commission this week wrote that the attack on MBC Network's studios heralded "gloomy predictions of things to come in the very near future to a country already bedeviled by lawlessness, violence and corruption."

"In less than 48 hours this prediction has unfortunately proved true," it said in a statement. (Editing by Jerry Norton)

AlertNet news is provided by