BAGHDAD — Iran today re-opened five border crossing points with Kurdish-run northern Iraq, closed last month by Tehran to protest the American detention of an Iranian official as the Americans step up allegations that the Iranians are fueling the violence in Iraq.

The border points were closed to protest the American detention of an Iranian official who the military said was a member of the paramilitary Quds Force, a branch of the Iranian Revolutionary Guards that is accused of provide arms and training to Shiite extremists.

Ratcheting up the rhetoric, top American commander General David Petraeus claimed this weekend that the Iranian ambassador to Baghdad, Hassan Kazemi Qomi, was a member of the Quds Force.

“The Quds Force controls the policy for Iraq; there should be no confusion about that either,” General Petraeus told CNN and other reporters during a trip to a military base on the Iranian border. “The ambassador is a Quds Force member. Now he has diplomatic immunity and therefore he is obviously not subject and he is acting as a diplomat.”

General Petraeus did not provide details on how he knew Mr. Qomi, who has held talks in Baghdad with American Ambassador Ryan Crocker, belonged to the Quds Force, and the Iranian Foreign Ministry rejected the allegations.

“These are not new comments. Similar accusations were raised, formerly. It is baseless and not right,” a ministry spokesman, Mohammad Ali Hosseini, told reporters in Tehran.

The Iraqis have found themselves caught between two allies as they struggle to balance the interests of their main sponsor the American military and Iran, a major regional ally. Iran holds considerable sway in Iraq as both countries have majority Shiite populations and many members of Prime Minister al-Maliki’s ruling Shiite bloc have close ties with Tehran.