The previous meeting on May 28 marked a break in a 27-year diplomatic freeze and was expected to have been followed within a month by a second encounter.
But following that meeting, the US said Iran had not scaled back what Washington alleges is a concerted effort to arm fighters and harm US troops.
Tensions also have risen over Tehran's detention of four Iranian-American scholars and activists charged with endangering national security.
The US has demanded their release, saying the charges against them are false.
At the same time, Iran has called for the release of five Iranians detained in Iraq, whom the US has said are the operations chief and other members of Iran's elite Quds Force, which is accused of arming and training fighters in Iraq.
Iran says the five are diplomats in Iraq with permission from the government.
On Sunday, US troops detained two suspected weapons smugglers who may be linked to Iran's elite Quds Force, the military said.
It said the suspects and a number of weapons were seized during a raid on a rural farm compound in eastern Iraq, near the Iranian border.
Sean McCormack, a spokesman for the US state department, said the US wanted to use the meeting to warn Iran against continuing its support for fighters, but offered no explanation for the apparent change of heart about meeting Tehran.
Visas for Iraqis
Meanwhile, the US ambassador in Baghdad, Ryan Crocker, has asked the Bush administration to offer visas to Iraqis who are helping the US government.
More than 100,000 Iraqis are employed by US-led forces and there are fears they will quit without a guarantee of asylum.
The US has so far lagged in its pledge to admit 7,000 Iraqis, with only 133 granted visas since last October.