Afghanistan has taken positive steps to fight its massive illegal drugs trade but it remains to be seen whether they would make a dent in this year's opium crop, the U.N. anti-narcotics chief said.

Last year, Afghanistan produced an estimated 4,200 tons of opium, enough to make 420 tons of heroin _ nearly 90 percent of global supply.

"I expect some reduction" this year, Antonio Maria Costa told The Associated Press in an interview Thursday. "I don't know whether it's going to be significant ... We just don't know yet."

His assessment was more cautious than Afghan President Hamid Karzai, who told the European Union in Brussels on Thursday that poppy production would decline by between 20 and 30 percent this year.

The U.S., Europe and other countries have pledged hundreds of millions in counternarcotics aid amid fears that newly democratic Afghanistan _ once a haven for al-Qaida _ is becoming a "narco-state."

Costa, executive director of the U.N. Office on Drugs and Crime, said a combination of government policy and declining market prices after bumper crops in recent years had persuaded many farmers not to plant poppy _ from which opium originates _ this year. ADVERTISEMENT

But an estimate of the crop would only be possible when a survey was complete in August or September.

He appealed for more foreign aid to help farmers grow alternative crops. He said international donors have so far only disbursed a third of the assistance they promised.

"For sure, eradication is crucial. Everybody including farmers has to respect the law," Costa said. "But Afghanistan is among the poorest countries in the world and opium is the single most remunerative crop. My call is for donors and countries to provide development assistance to farmers."

He said the Afghan government had issued arrest warrants against major traffickers and taken action against some corrupt officials implicated in the illicit trade, estimated to be worth about US$2.8 billion _ gradually making it more difficult for traffickers to operate.

Costa said Pakistan _ which has a 2,430-kilometer (1,520-mile) border with Afghanistan _ was "very exposed" to the trade and was playing an important role in fighting it. He met Pakistani President Gen. Pervez Musharraf on Thursday.

As well as being a key route for the smuggling drugs out of Afghanistan to addicts in the Middle East and Europe, he said there was also evidence that precursor chemicals needed to refine opium into heroin were being smuggled through Pakistan into Afghanistan.

Pakistani officials say they seized 15 tons of heroin and morphine base in the first four months of the year, and are calling for more international assistance. The country's anti-narcotic force has an annual budget of only about US$2 million.