A U.N. employee used U.N. diplomatic pouches to smuggle illegal drugs as part of a ring that brought 25 tons of contraband into New York in the past year and a half, federal prosecutors and the FBI said yesterday.

The shipments of khat — an illegal stimulant grown in East Africa — were received by a mail clerk employed by the United Nations, Osman Osman, who sent them across America, according to an indictment unsealed yesterday.

Prosecutors say Mr. Osman, a Somali citizen who had been employed at the United Nations for 29 years, was an important cog in the largest khat trafficking enterprise America has known. Forty-four defendants were named in yesterday’s indictment, and 14 were still at large, a spokeswoman for the U.S. Attorney’s office said.

Khat is an evergreen shrub grown along the Horn of Africa. Chewing the leaves has long been a custom in the countries of the region. Immigrants have brought the habit to America, where the active chemical in the leaf is as illegal as heroin. The trafficking ring exposed yesterday was responsible for importing more than $10 million worth of khat since the end of 2004, according to the indictment. A portion of the proceeds were sent back to Europe and the United Arab Emirates, in order to repay khat producers, according the indictment.

At a press conference yesterday, an FBI agent, Mark Mershon, said law enforcement officials hoped those arrested would cooperate with efforts to track down exactly where that laundered money went. The U.S. Attorney in Manhattan, Michael Garcia, said that the khat trade is a known source of funding for Somali warlords.

Several shipments of the drug entered this country through U.N. diplomatic pouches, while other bundles of khat were carried on trans-Atlantic flights, or shipped by mail, according to the indictment. From New York, khat dealers distributed the drug across the country, according to the indictment.

In Columbus, Ohio, home to one of the country’s largest Somali communities, a police officer said he had heard of yesterday’s bust and was not at all surprised by the proportions of the khat trade in this country.

The sergeant with the narcotics division in Columbus, Ben Casuccio, said that the department has been interdicting khat since the mid-1990s. He noted the difficulty that police had in preventing khat from being sold in coffee houses within the tightly-knit Somali community of Columbus. But Mr. Casuccio said his primary worry was not the local effect of the khat trade.

“Here is our concern — there is an illegal government in Somalia currently and it’s being run by warlords,” Mr. Casuccio said, by telephone. “The funds are being sent back to facilitate those folks. We feel that some of the funds from khat are being sent back to these terrorist warlords.”

Khat, which is chewed or brewed as a tea, causes euphoria, but can also lead to heart disease and violent outbursts, the indictment said.

The director of the Somali Justice Advocacy Center in St. Paul, Minn., Omar Jamal, said that khat is taken socially in large segments of the Somali community, where it is seen as no more harmful than the “the average American buying a cup of coffee.”

“This is what people do when they sit around and talk,” he said.

About half the people charged in the indictment do not live in New York, according to law enforcement officials. Mr. Osman, the U.N. mail clerk, is listed in the indictment as one of four leaders of the organization. He pleaded not guilty late yesterday afternoon in U.S. District Court in Manhattan. His lawyer is currently driving in from Ohio, said the attorney who represented him at the arraignment, David Gordon.

A spokeswoman for the U.N., Marie Okabe, confirmed that Mr. Osman has worked at the U.N. since 1977, but declined to provide further details of what role, if any, the mail room at Turtle Bay played in the drug trafficking. Mr. Osman, 47, lives in Rocky Hill, Conn., according to a spokeswoman for the U.S. Attorney’s office.

The indictment suggests that “Operation Somalia Express,” as the investigation was called, put an end to a well-organized criminal enterprise that was willing to use violence. One of the men charged, Bashi Muse, spoke of killing a customer who owed him money, according to the indictment. Khat trafficking charges carry a maximum sentence of 20 years in prison, although five of the defendants face additional money laundering charges, which also carry a potential 20-year sentence.