Admiral Mike Mullen, the highest-ranking US officer, expressed his concerns on Tuesday, a day after the Wall Street Journal reported that the Pentagon was considering establishing a military hot line with Tehran.
"We haven't had a connection with Iran since 1979. Even in the darkest days of the Cold War, we had links to the Soviet Union," Mullen told the Carnegie Endowment for International Peace.
"We're not talking to Iran so we don't understand each other. If something happens, it's virtually assured that we won't get it right, that there will be miscalculations which would be extremely dangerous in that part of the world."
The United States has grown increasingly concerned about Iran's alleged regional ambitions in recent years as Tehran has pressed ahead with its nuclear enrichment program, which Washington fears is aimed at creating atomic weapons.
Iran insists its nuclear program is entirely peaceful, but its support for armed groups like Hamas and Hezbollah and its leaders' harsh rhetoric on Israel have raised concerns in the West that it could plunge the region into turmoil.
The Wall Street Journal reported earlier this week that the United States was especially worried about a fleet of speedboats that often challenge US and allied warships in the Persian Gulf.
The high-performance Iranian vessels are likely controlled by the Islamic Revolutionary Guard Corps, Tehran's elite military force, and can be equipped with missiles.
In recent months, a British destroyer fired warning shots at one of these boats as it appeared to be preparing to ram the larger ship, and Iranian aircraft have also challenged US ships, the Journal said.
The United States has not had diplomatic relations with Iran since its 1979 revolution, during which Islamists seized the US embassy in Tehran and held 52 diplomats hostage for more than a year.