The Middle East has always been a labyrinth of swiftly changing partnerships, and never more so than in Iraq today.
Start with the unlikely alliance that has made possible the lightning gains of the Islamic State in Iraq and the Levant (ISIL) this week in Iraq's Sunni heartland.
By all indications, the ISIL is cooperating militarily with a reborn version of Iraq's former ruling Ba'athist Party.
Residents of Mosul say that the Islamist fundamentalists and the Ba'athists -- who have diametrically opposed ideologies -- took the city together.
"I object to saying there is just the Islamic State in Iraq and the Levant here," one man told Radio Free Iraq privately by phone from Mosul on June 12.
"Those who entered the province of Nineveh are a mixture of the former army, the Ba'athists," and other militant Iraqi Sunni groups along with the ISIL, he said.
Kirk Sowell, a Jordan-based political-risk analyst who publishes "Inside Iraqi Politics," says that the reinvigorated Ba'athist Party, known as the Jaysh Rijal al-Tariqah al-Naqshabandia (JRTN), and the ISIL have already previously worked together in Fallujah, where they have been battling government troops since January.
"As long as they are still fighting Baghdad, as long as they are still fighting the Iraqi security services, they appear to be getting along, and this should not be a surprise to anyone because they have been getting along in Fallujah for five months," he notes. "But assuming that the army does not take back Mosul quickly, the question is how long that [cooperation is] going to last. I suspect only so long, because ultimately the ISIL and the JRTN are incompatible."
During the Saddam era, the secular Ba'athist Party ruthlessly exterminated any opponents who challenged its absolute grip on power, including religious critics. The ISIL, which envisions creating a Islamist caliphate in Iraq and the Levant, has an equally brutal reputation for executing anyone who rejects its strictly fundamentalist authority.
The two sides have yet to try jointly controlling territory and sharing power -- Mosul, Tikrit [Saddam Hussein's hometown], and their other recent gains could now pose a challenge for them in this respect.
Still, the ISIL and the Ba'athists are not the only odd couple in Iraq today. In the face of their sudden advance, Iran and the United States, too, suddenly find themselves lining up against a shared enemy.
Reacting to the ISIL's advances, Iranian President Hassan Rohani vowed on June 12 that Tehran will combat the group's "violence and terrorism."
"This is an extremist, terrorist group that is acting savagely," Rohani said live on state television
Iran's Tasnim news agency on June 13 quoted a leading military official, Brigadier-General Mohammad Hejazi, as saying Tehran was ready to supply Iraq with "military equipment or consultations."
Tehran regards the ISIL as a danger to two of its regional allies -- Iraqi Prime Minister Nuri al-Maliki in Baghdad and Syria's President Bashar al-Assad -- and as a threat to Shi'ism, Iran's state religion, which Sunni fundamentalists consider heresy.
Washington, too, has not minced words regarding the ISIL.
U.S. President Barack Obama said June 12 that Washington considers "all options" open for helping Maliki fight back.
"I don't rule out anything, because we do have a stake in making sure that these jihadists are not getting a permanent foothold," Obama said.
Washington sees the ISIL as a threat to Maliki and as global jihadists who have spun off from Al-Qaeda and share its vehemently anti-Western ideology.
But if Iran and the United States are each vowing to help Maliki combat the ISIL, it remains to be seen whether having a common enemy can lead them to any form of cooperation.
Sowell says Washington views Iran as playing a negative role in Iraq by funding Iraq's Shi'ite militias.
"The Iranian influence is through the militias and their impact is pernicious," Sowell notes.
Over the past six months Shi'ite militias have carried out attacks in mixed areas around Baghdad, particularly in Diyala province between Baghdad and the Iranian border.
Analysts say the militia attacks have helped to inflame Sunni public opinion
and contributed to the motivation of Sunnis to take up arms or acquiesce in the current ISIL offensive.
Iran, meanwhile, accuses Washington of contributing to the violence in Iraq by providing support to Syrian rebels fighting Damascus. Washington denies the charge, saying it only provides non-lethal aid and provides nothing to extremist groups like ISIL.
Still, the recent gains by ISIL this week may alarm both Washington and Tehran enough to stir thoughts of possible cooperation.
A senior Iranian official told the Reuters news agency on condition of anonymity on June 13 that the possibility of cooperation with Washington is being discussed internally among the Islamic Republic's leadership.
"We can work with Americans to end the insurgency in the Middle East," the official said, referring to events in Iraq. "We are very influential in Iraq, Syria, and many other countries."