KABUL, Afghanistan - Iranian weapons have begun flowing into Afghanistan, Defense Secretary Robert Gates said Monday, but he and Afghan President Hamid Karzai agreed involvement by Tehran cannot yet be proved.

Gates told a news conference at the presidential palace that he and Karzai had discussed the Iranian weapons issue.

"There have been indications over the past few months of weapons coming in from Iran," Gates said. "We do not have any information about whether the government of Iran is supporting this, is behind it, or whether it's smuggling, or exactly what's behind it."

The Iranian weapons are being supplied to the Taliban insurgents, he said, adding that some may also be headed to criminals involved in Afghanistan's drug trade. Gates did not specify what types of weapons were involved.

A NATO spokesman told reporters last week that a powerful type of roadside bomb like those used in Iraq, was found recently in Kabul. The bomb, never before seen here, is known as an EFP, or explosively formed projectile. It was notable for its level of sophistication and has characteristics similar to the type in Iraq that have borne Iranian manufacturing markings.

Asked separately whether he believed Tehran was behind the flow of weapons, Karzai suggested it was unlikely.

"There's no reason that any of our neighbors should support the Taliban," Karzai said. "We don't have any such evidence so far" regarding possible Iranian government involvement, he said, adding that relations between the two nations were improving.

"Iran and Afghanistan have never been as friendly as they are today," Karzai said.

At the news conference, Gates also said U.S. commanders have been relieved that an expected spring offensive by the Taliban has been less intense than some feared. He said it was thwarted by an "Afghan alliance offensive that has put the Taliban off their game."

Gates later flew to the southern city of Kandahar, accompanied by Abdul Rahim Wardak, the Afghan defense minister. They held closed meetings with senior American commanders, including Maj. Gen. Robert Durbin, who is in charge of training Afghan security forces, and British Maj. Gen. Jacko Page, the top NATO commander for southern Afghanistan, where the Taliban was expected to make a strong push this spring.

In their joint news conference in Kabul, Gates and Karzai said they regretted the number of American air strikes that have taken the lives of innocent Afghan civilians, and they pledged to work together to reduce such incidents.

Gates, while acknowledging the problem, said the Taliban share blame for deliberately placing civilians at risk in order to stir sentiment against the American military and the Afghan government.

"Avoiding civilian casualties is very important in terms of winning the loyalty and the support of local populations," Gates said. "At the same time, I think it is important to stress ... that the Taliban deliberately puts civilians in harm's way."

Earlier in the day, during a stop at Camp Morehead, the head of the Afghan National Army said his country is pushing the United States to accelerate training and equipping his army so the Afghans can fight the Taliban on their own.

Gen. Bismullah Khan, the army chief of staff, told reporters traveling with Gates that the goal of attaining independence on the battlefield is essential.

"We don't have air support," he said through an interpreter, expressing frustration at the lack of an Afghan air force. "That is a very serious problem. We are looking forward to the day when we can fight the enemy independently."

He was asked how soon the army could reach that goal.

"We asked for it to be as soon as possible," he said. "I will ask the secretary of defense to expedite the process so we can do this. The only way to defeat the enemy is to become independent."

He mentioned that the United States has committed, with the help of allies, to building an Afghan national army of 70,000 soldiers by the end of next year.

"But it's not going to be enough," he said. "We'll ask for more."

Gates, making his second visit to Afghanistan as defense secretary, came to this training camp some five miles southwest of Kabul to confer with U.S. and Afghan commanders training Afghan special forces. Despite a rise in insurgent violence this spring, Gates said he remains convinced American and NATO forces are making steady progress against the Taliban.

For months, Gates has expressed concern about possible reversals in Afghanistan, which still lacks a self-sustaining military and suffers from the unmet expectations of building an effective central government.