La Paz, Bolivia (CNN) -- Bolivian leader Evo Morales says he's worried that U.S. authorities will plant something on his presidential plane to link him with drug trafficking when he attends Wednesday's United Nations General Assembly meeting.

"Do you know what? I think they have to be preparing something," he told a convention of female farm workers over the weekend. "So much that I'm afraid to go with our airplane to the United States. Surely when we arrive, they can plant something and detain the presidential plane."

Morales said he was still planning to attend the meeting, but feared a U.S. plot.

"They are preparing something to discredit us with drug trafficking," he said.

The U.S. Embassy in La Paz declined to comment on Morales' assertions. But some opposition Bolivian lawmakers criticized the president's proclamation.

"The president has to understand that these types of messages are not good, because he who has not done anything wrong has nothing to be afraid of, and when the president shows these fears it makes the population worry and it harms his international image," Rep. Jaime Navarro said.

But Morales' supporters said political opponents have long used such strategies to bring down his government.

"They have always tried to harass the president, since he was a lawmaker they wanted to connect him with drug trafficking and they never could prove anything, and he has always faced the accusations," Rep. Edwin Tupa said. "And now that he's president, it isn't an accident that anyone, especially the U.S. government, would try to ruin his image."

Bolivia and the United States have had diminished relations since September 2008, when each country expelled the other's ambassador. Morales, a strong proponent of the cultivation of coca plants -- the source of cocaine -- expelled the U.S. Drug Enforcement Administration a month later. He also delivered a strong verbal criticism of the U.S. government at the United Nations General Assembly that year.

Journalist Gloria Carrasco contributed to this report.