KABUL - A Romanian officer was killed in a roadside blast Tuesday in southern Afghanistan, where a day earlier rockets killed a Dutch soldier and wounded five others, officials said.

The Romanian vehicle patrol was hit by a roadside bomb northeast of Qalat, the capital of the southern Zabul province, killing the officer and wounding four other troops, the Romanian Defense Ministry said in a statement.

On Monday, in neighboring Uruzgan province insurgents fired rockets at the Netherlands' main base there, killing a Dutch soldier and wounding five others, said Gen. Peter van Uhm, the Dutch defense chief. The base had come under fire by Taliban fighters regularly in the past, but the latest attack was the first to cause causalities.

The Dutch and Romanian troops all served as part of the NATO-led force.

Southern Afghanistan is the center of the Taliban-led insurgency, where thousands of new U.S. troops were ordered to join the fight by President Barack Obama to try to reverse militant gains of the last three years.

Coalition troops, meanwhile, killed four suspected Taliban militants and detained two others following a raid on a bomb-making cell in neighboring Kandahar province Monday, the U.S.-led coalition said in a statement.

The four men were killed "during the engagement" after they attempted to barricade themselves inside a compound in Maywand district, the statement said.

The latest violence comes as the top U.S. and NATO commander in Afghanistan, Gen. David McKiernan, said that despite the arrival of 21,000 new U.S. troops this year, it will be years before Afghan forces can be in charge of security.

McKiernan also said his troops had increased targeting of drug operations eight- or 10-fold in the past four months, specifically for drug lords or operations that could be tied to insurgents and insurgent funding.

Afghanistan is the world's largest producer of opium, the main ingredient in heroin. The Afghan drug trade accounts for 90 per cent of worldwide production. The UN estimated last year that up to $500 million from the illegal drug trade flows to Taliban fighters and criminal groups.

McKiernan told newspaper executives gathered at The Associated Press annual meeting Monday that heroin trafficking was "a debilitating system across this country, that eats away at good governance, eats away at progress and it certainly provides a funding source for the insurgency."