Much of the media have portrayed the latest battles for Basra, and attempts by armed groups to undermine the recently improved security in Baghdad, as a power struggle among rival Shiite factions.

In this analysis, three Shiite factions - the Fadila (Virtue), the Dawa (The Call) and the Islamic Supreme Council of Iraq - that support Prime Minister Nouri al-Maliki's coalition government are trying to disarm the remnants of the Mahdi Army of the elusive mullah Muqtada Sadr.

But that explanation has several problems.

To start with, it is the regular Iraqi army - not any Shiite armed faction - that is doing the fighting in Basra. To underline that point, Maliki went to Basra to supervise operations personally.

And the kind of fighting witnessed in Basra is different from the usual militia operations.

This is a war of position, with units acting as detachments of a regular army trying to deny the Iraqi government forces control of specific territories. The fighters defying the Iraqi army may be Iraqi irregulars, even nominal members of the Mahdi Army - but those leading them are acting as textbook regular-army commanders.

At least some of the officers in charge of the rebel units may be seconded from Iran's Islamic Revolutionary Guard Corps as part of a broader plan to control the Basra region, and thus the lifeline of the Iraqi economy.

This wouldn't be the first time that Guard officers and NCOs have fought at the head of native fighters outside Iran. Two years ago, Guard personnel played a crucial role in the war between the Lebanese Hezbollah and Israel. And Guard officers and NCOs led some armed Iraqi groups in operations against Saddam Hussein during the Iran-Iraq war in the 1980s.

The type of weapons used in both Basra and Baghdad also suggests at least some outside involvement. The rebels in Basra are using a large number of armored vehicles to move men and materiel around - something no other Shiite militia, and certainly not the Mahdi Army, had ever done. They're also using heavy artillery, mobile rocket launchers and a sophisticated communications system unavailable to militias.

Elements of the Mahdi Army may provide the visible face of the rebellion, but there is no evidence that the militia (supposing it even still exists as an organized force) is the sole star of this show.

Sadr, after all, has extended the ceasefire he declared six months ago - and, in a recent letter, admitted that he had failed to "liberate" Iraq and create an "Islamic society." Last week, he issued another statement calling for a political settlement in Basra - a far cry from the bellicose noises made by these rebels with the help of Iranian state-owned media.

Spending most of his time in Iran, Sadr is now preparing to claim a theological position within the Shiite hierarchy - an ambition that cannot be realized through gunfights in the streets of Basra and Baghdad.

One other notable fact: Whoever is running the show on the rebel side has been able to devise a battle plan that included simultaneous attacks along a north-south axis that includes Baghdad, al-Amarah and Basra. No other Iraqi militia group, Shiite or Sunni, has had the resources to stage such a campaign before.

The rebels are trying to retain areas that connect Basra, a vast urban sprawl, to the Shatt al-Arab, an estuary that forms part of the border between Iran and Iraq. If the Iraqi government is kept out of these areas, Iran would control both banks of the strategically vital waterway. Iran has already occupied several islands in the waterway facing Basra, using them as advance observation posts.

Finally, the design of this operation recalls an Iranian plan, drafted in 1983-84, to seize control of Basra and parts of the Shiite-majority areas of southern Iraq.

According to Ibrahim Yazdi, once a top adviser to the late Ayatollah Khomeini, the "Basra Plan" was devised as a compromise. The ayatollah wanted the war with Iraq to continue until the fall of Baghdad, after which he hoped his armies would march on Jerusalem. His advisers, including Yazdi, knew that Iran could not win such a war and tried to placate him by offering him Basra.

Visitors to Basra since Saddam's fall have often been struck by the massive "Iranian" presence there. Much of this consists of large numbers of Iraqi Shiites, known as mua'aweddin (returnees), who have come home after years of exile in Iran. There are also those who hold both Iranian and Iraqi nationality. Known as muzdawajun (double nationals), they are often accused of being loyal to Shiism rather than any secular concept as a nation state.

Why has Basra, a relatively calm place for the last five years, heated up now?

One reason may be the British decision last year to withdraw from the city. This left a vacuum that the new Iraqi army and police were unable to fill immediately. Iran may have seized the opportunity to try to grab as much influence and presence as it could - both via Shiite militias (including the Mahdi Army) that it has financed for years and by sending large numbers of operatives across the border.

The prospect of losing control of Basra may have prompted the Maliki government to act. Whoever controls Basra could influence the outcome of next year's crucial local-government elections. Basra and the Shiite south represent the backbone of support for the Maliki coalition; without them, the coalition couldn't retain control of the central government in Baghdad.

At a time when US commanders in Iraq, including Gen. David Petraeus, openly accuse Iran of having joined the Iraqi imbroglio, the fate of Basra appears important for another reason.

If there were a war between the United States and the Islamic Republic, one likely early US objective would be seizure of Iranian oilfields. To do that, America and its allies would need advance bases in southern Iraq - the key to which is Basra. Iran, on the other hand, could extend the defensive perimeter of its oilfields by annexing Basra.

Both sides may simply be interested in testing the waters at this stage. But the war over who will shape the future of Iraq, indeed of the Middle East as a whole, is in its early stages.