Karbala (AsiaNews/Agencies) – Iraqi security forces are on high alert in Karbala, where thousands of Shiite pilgrims have been gathering for the festival of Shabaniya in defiance of recent threats of 'total war' made by al-Qaeda in Iraq leader Abu Musab al-Zarqawi, threats condemned on the week-end by some Iraqi Sunni leaders.

For this morning's early hours, Shiite pilgrims have been praying in the mosques of the Holy City celebrating the birth of imam al-Mahdi, the 12th and last imams and successor to the prophet Muhammad.

Thousands of police officers and soldiers have been deployed along with coalition forces to protect the city, which is south of Baghdad. Cars have been barred from entering the city to reduce the risk of attacks, whilst arriving pilgrims are searched. Local hospitals are on high alert and a blood drive is underway among residents.

There is great fear that Sunni extremists may try to strike at the religious gathering to set off a civil war. Since September 14, terrorists have killed more than 260 people, mostly Shiites.

Last week, a month from the country's controversial constitutional referendum, al-Qaeda in Iraq leader Abu Musab al-Zarqawi had vowed "total war" against Iraq's Shiites.

However, pilgrims reaching Karbala have not been frightened away and seemed determined to take part in the festivities. "His [al-Zarqawi's] threats won't stop us from participating in the celebrations," a man on his way from Baghdad said.

Sheik Mahmud al-Sumaidaei, leader of the Baghdad-based Sunni Association of Muslim Scholars condemned Jordanian-born Abu Musab al-Zarqawi and his foreign fighters, saying Iraqi Sunni resentment against them is growing, because the al-Qaeda-linked group has repeatedly used Iraq's sectarian tensions and division to try to achieve its own goal of killing all Shiite Muslims in the region.

Recently, another leading cleric of the Association, Saleh Mahdi Abid, called attacks against Shiites inhuman, and said that Zarqawi was not defending the interests of Iraqi Sunni Arabs when he unleashed terror on the Iraqi people.

Shiite leaders led by populist cleric Muqtada al-Sadr urged Sunnis on Sunday to take a tough stand against rebels in the face of al-Zarqawi's declaration of war.

Al-Sadr spokesman Abd al-Hadi al-Darraji said the influential Association of Muslim Scholars should take more decisive action against those inciting civil war.

"We want them to issue a fatwa (religious edict) forbidding Muslims from joining these groups that deem others infidels," he said. "This will be crucial in ending terrorism."