In addition, although the mosque is revered by Shi'a Muslims, it does not have the special protection of inclusion on the World Heritage List maintained by the United Nations Educational, Scientific, and Cultural Organization (UNESCO).
These factors, plus the approval for attack given by the governor of Al-Najaf, appear to lower the legal barriers to an all-out assault on the site.
U.S. forces today launched what they called "major operations" in the center of Al-Najaf. But a U.S. military spokesman said the operations were not focused on the mosque.
UNESCO also hopes a major battle can be averted at the gold-domed shrine of Imam Ali Ibn Abi Talib, who was leader of the Shi'a. A deputy assistant director-general for culture at UNESCO, Milagros del Corral, tells RFE/RL her agency has continued to remind the warring sides to cease fighting around the shrine: "It is a very, very difficult situation, and very worrying too. Let's hope that the Najaf thing can be fixed with no further risk for the places there."
An official designation on the World Heritage List carries special obligations for warring parties to preserve and protect culturally important sites. Only two sites in Iraq are on the list -- the ancient centers of Hatra and Ashur. But the country has numerous culturally significant sites.
Del Corral says UNESCO gave the U.S.-led coalition a list of sensitive sites prior to the start of war in March 2003, including the Imam Ali Mosque. With the exception of the unchecked looting at Iraqi museums last year, she says the coalition has taken "maximum care" to protect important cultural sites: "Of course, in a conflict like that you cannot pretend that everything will be untouched but [the coalition] asked and obtained the necessary information, and they tried to respect it the best they could."
Iraq is party to the 1954 Hague Convention for the Protection of Cultural Heritage in the Event of Armed Conflict, the main international instrument to curb abuses at key cultural sites.
A protocol was added in 1999 following the widescale destruction of culturally significant sites in many of the wars of the 1980s and 1990s.
The 1999 protocol says that when cultural property is used as a military objective, it loses its claim for special protection. Even under such conditions the measure urges parties to avoid damage to the property. Iraq has not yet acceded to the protocol.
The United States is not a party to either instrument, but says it generally observes the Geneva Conventions on limiting war actions to legitimate military targets.
Daniel Helle is a legal expert with the International Committee of the Red Cross and is deputy chief of its mission to the UN in New York. He tells RFE/RL that the protection of culturally important sites during war is one of the most difficult parts of international humanitarian law to monitor.
Such law, he says, is fundamentally interested in the distinction between civilian and military objectives. But if places like hospitals, trains, or churches are used for military purposes by one side, he says, the distinction is blurred: "The idea is that you limit your attacks only to military objectives. But, of course, it's not only the attackers' responsibility. It's also the one defending who has the responsibility of distinction."
During a previous round of fighting in Al-Najaf in the spring, chief Shi'a cleric Ayatollah Ali al-Sistani called on both U.S. forces and radical cleric Muqtada al-Sadr's militants to keep out of Shi'a shrine cities.
Al-Sistani is currently in London for treatment of a heart condition. His absence may have emboldened U.S. military commanders to expend an all-out effort to try to seize al-Sadr in Al-Najaf, says Juan Cole, a professor of modern Middle Eastern history at the University of Michigan.
But Cole says the United States is in a no-win situation, in part because al-Sadr's militia would be seen as defending sacred ground against an occupying force. Any marked escalation in the Al-Najaf area, he says, would intensify anger against the United States among even moderate Shi'a, and undermine the caretaker government.
Cole tells RFE/RL that a U.S. capture of al-Sadr may prove a short-term victory: "They'll get what they think they want, but I think at a cost of alienating -- deeply, deeply alienating -- not only the Iraqi Shi'ites, but Shi'ites around the world."
A cease-fire negotiated after fighting with al-Sadr's forces in the spring established an "exclusion zone" for U.S.-led forces around the mosque and vast cemetery nearby. U.S. commanders say al-Sadr's militia violated the agreement by using the area clearly for military purposes.