HERAT, Afghanistan — From cheap ice cream to 24-hour electricity, Iran is strengthening economic ties with western Afghanistan that could undermine support for American and NATO forces.

Western Afghanistan has a newly paved 75-mile stretch of highway between the Iranian border and its main city, Herat, courtesy of the Islamic republic. Iran is also considering building a rail line on the busy route, and the nation has pledged another $560 million to help rebuild Afghan infrastructure and businesses.

“Iran is not going away from here,” a Herat-based Western diplomat said. “The question is whether we can coexist in this region together and realize that some of our aims might even be the same when it comes to Afghanistan.”

Tehran has built 10 schools and built several clinics in western Afghanistan, and paid for the equipment to provide electricity 24 hours a day in Herat, unlike in most other parts of the country, including the capital, Kabul.

Iranian influence here dates back to ancient times and, while dependent on American military and financial support, the Afghan government tries not to antagonize Iran, which currently houses about 2 million Afghan refugees.

“Our hope is for Afghanistan to be peaceful and stable because that would be good for the region,” an Iranian diplomat in Kabul said, speaking on condition of anonymity because he was not authorized to speak with the media. “Everyone wants a stable neighbor.”

If Iran and America are at odds, Defense Ministry spokesman General Zahir Azimi said, “We will stay out of it.”

Local political analyst Mohammed Rafiq Shaeir says Iran wants greater influence in western Afghanistan to promote its own national interests, both security and economic.

“The people of Herat have doubts about why Iran is putting so much attention into this area, but they still recognize that it is good for our own national interests and security in the region to have friendly relations with Iran,” Mr. Shaeir said.

A prominent political analyst in Tehran, Saeed Laylaz, said Iran is investing in Afghanistan chiefly for its own national interests, rather than to counter Western influence.

“Regardless of presence of the NATO forces there, Iran has been always suffering from lack of stability in Afghanistan,” Mr. Laylaz said in a phone interview. “An unstable Afghanistan would cause difficulties for Iran.”

For many people in this historic city, famous for its mosques and minarets, Iran’s largesse is a mixed blessing.