By Claudia Parsons

UNITED NATIONS, Oct 15 (Reuters) - A U.N. envoy on Monday urged countries with troops in Afghanistan to resist the temptation to reduce their roles, saying security still was a challenge and the Afghan police was plagued by corruption.

Reporting to the U.N. Security Council, special representative for Afghanistan Tom Koenigs said while there was a dip in violence in the last two months, the number of violent incidents was still up 30 percent from last year.

"The sad result is a significant increase in the numbers of civilian casualties -- at least 1,200 have been killed since January this year," Koenigs said, noting the United Nations had recorded 606 roadside bombs and 133 suicide attacks, up from 88 suicide bombs by the same time last year.

Koenigs said the Afghan army should be up to a strength of 70,000 by the end of the year, but development of the police force was more difficult because of "a culture of patronage and corruption" stemming from the interior ministry.

"For the time being we must recognize that ISAF represents the most capable defense of the government against the insurgency," he said, referring to the NATO-led International Security Assistance Force (ISAF).

"Because of this, nations should resist the temptation to reduce their commitment. Now is not the time to wobble," he said.

U.S. deputy ambassador Alejandro Wolff said Afghanistan was going through a "critically important and difficult transition" and security was still an enormous challenge.

Wolff urged the international community to "dig deep" to maintain financial support for rebuilding Afghanistan.

Representatives of a string of countries, from Britain to Iran, expressed concern about Afghanistan's poppy production hitting a record high this year and about links between drugs traffickers and Taliban insurgents.

Afghanistan produced some 8,200 tonnes of opium in 2007, or 93 percent of the world's supply, according to U.N. figures.

"A disjointed international community approach, combined with a lack of Afghan leadership at the national and sub-national levels, has allowed drug traffickers to prosper," Koenigs said.

Afghan Ambassador Zahir Tanin said Afghanistan could not act alone to fight drugs. "Real progress towards reduction and elimination requires a more robust effort from the transit and consuming countries," he told the council.

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