The tanker was seized in the evening by agents with the American-trained border protection force at the Iraqi town of Badra, after crossing at Munthirya on the Iraqi border, the official said. According to the Iraqi official, the border police found several thousand partly completed ballots inside.
Today, Adel Al-Lami the director general of the electoral commission, said he "dismissed" the reports, asserting that such news is "part of the electoral campaign." Nevertheless, an official in Diyala province said of the reports of the forged ballots, "I am sure 100 percent of the authenticity of this news."
"It is not just this truck, there were other trucks trying to cross the borders also in Shalamcha," he said, speaking on condition of anonymity.
Interior ministry officials also confirmed the reports. One official, who spoke on the condition of anonymity because he was not authorized to speak publicly, said the Iranian truck driver told the police under interrogation that at least three other trucks filled with ballots had crossed from Iran at different spots along the border.
The official, who did not attend the interrogation, said he did not know where the driver was headed, or what he intended to do with the ballots.
The seizure of the truck comes at a delicate time in Iran's relations with both Iraq and the United States. The American government has said Iranian agents are deeply involved in trying to influence events in Iraq, by funneling money to Shiite political parties and by arming and training many of the illegal militias that are bedeviling the country.
Agents of the Iranian government are believed to be supporting the two main Shiite political parties here - the Supreme Council for the Islamic Revolution in Iraq and the Dawa Party -with money and other assistance. Both parties support a strong role for Islam in the Iraqi state; however, compared with the Iranian government itself, which is a strict theocracy, the Iraqi version is relatively moderate.
In recent months, American officials in Baghdad and Washington, along with their British counterparts, have contended that sophisticated bombs have been smuggled across the border from Iran, and that some of them have been used against American and British soldiers. The bombs are thought to be far more sophisticated than most of the powerful but rather rudimentary ones used to attack American tanks and convoys here.
At a news conference on Tuesday, hours before the ballot seizure, the American ambassador in Baghdad, Zalmay Khalilzad, spoke of what he said were overt Iranian attempts to influence events in Iraq.
"Iraq is in a particularly difficult neighborhood," he said. "There are predatory states, the hegemonic states, with aspirations of regional hegemony in the area, such as Iran. There are states that fear success of democracy here - that it might be infectious and spread."
"We do not want Iran to interfere in Iraqi internal affairs," Ambassador Khalilzad said. "We do not want weapons to come across from Iran into Iraq, or training of Iraqis to take place."
Mr. Khalilzad has been authorized to speak with the Iranians on the subject of Iraq, but said Tuesday that he had not yet done so.
Northwest of Baghdad, four American soldiers were killed when their patrol struck a mine, the American military command said, offering no further details.
In a message posted on the Internet, the Islamic Army of Iraq, an insurgent group, claimed to have attacked an American convoy and killed a number of soldiers near Abu Ghraib, west of Baghdad. It was unclear whether the posting was referring to the same attack.
The same group posted another Internet message calling on resistance fighters to refrain from attacking polling stations on election day, to "save the people's blood." The group urged Iraqis to continue killing American soldiers.
"This does not mean that we approve of what is called the political operation," the statement said, referring to the election.
Both Islamic Army postings were translated by SITE, a Washington organization that tracks Islamic militant groups.
Khalid al-Khassan contributed reporting from Baghdad for this article, and Kirk Semple from Ramadi.