Iran's president said Tuesday he has "serious doubts" that his country is supplying weapons to Taliban insurgents in Afghanistan, refuting allegations by some Western officials that Iran is arming the militants. Speaking during his first-ever visit to Afghanistan, President Mahmoud Ahmedinejad called Iran's eastern neighbor a "brotherly nation" whose stability is paramount for the region. When asked if Iran is supplying weapons to the Taliban by a reporter from Voice of America, a U.S.-funded outlet, Ahmedinejad laughed and said the United States doesn't want Afghanistan and Iran to be friends. "The same allegation are made in Iraq. They are saying that they discover some weapons," Ahmedinejad said at a news conference with Afghan President Hamid Karzai. "What is the reason why they are saying such things? Iran is a big country. I have serious doubts about this issue." Ahmedinejad's trip comes a week after US President George W. Bush said during a news conference with Karzai last week in the United States that he thought Iran was playing a destabilizing role in Afghanistan, where the Taliban have stepped up attacks the last two years. The US military has charged that Iran is supplying weapons to Shiite militias in Iraq who are fighting against US troops there. Some Western and Persian Gulf governments have also alleged that the Islamic government in Tehran is secretly bolstering Taliban fighters. Among U.S. officials a prevalent view is that Tehran, while not an ally of the Taliban, is seizing any opportunity in both Iraq and Afghanistan to complicate US stabilization efforts. Former British Prime Minister Tony Blair wrote in a May edition of the Economist magazine that it is "clear" the Taliban is receiving arms from "elements of the Iranian regime." The top NATO commander in Afghanistan, US Army Gen. Dan McNeill, told The Associated Press in June that "I don't doubt that somewhere the Iranians may have helped the Taliban." Officials from NATO's International Security Assistance Force in Afghanistan have said they have no proof that top Iranian leaders have engineered or approved of weapons being supplied to the Taliban. Iran calls the accusation part of a broad anti-Iranian campaign and says it makes no sense that a Shiite-led government like itself would help the fundamentalist Sunni movement of the Taliban. Karzai praised Iran's role in Afghanistan, while the two leaders presided over the signing of a number of bilateral agreements in a number of fields, including security, counter-narcotics and agriculture. Ahmedinejad was accompanied in his trip by the Iranian foreign minister Manouchehr Mottaki, the secretary of Iran's Supreme National Security Council Ali Larijani and Mojtaba Samareh Hashemi, his top adviser. After his one-day stop in Afghanistan, Ahmedinejad is scheduled to travel to Turkmenistan to meet with the country's new president and then to Kyrgyzstan to attend the Shanghai Cooperation Organization.