BAGHDAD (Reuters) -- As Baghdad security improves and U.S. troops draw back, workers in cranes are removing mile after mile of giant concrete slabs put up to prevent the slaughter of innocents in sectarian fighting.

For Baghdad bookseller Abu Ali, it's too soon. Sitting in an alley surrounded by Shi'ite Muslim religious tracts, he recalls how his son was blown up by a massive bomb.

"Our security forces aren't experienced enough to maintain security by themselves," the 56-year-old told Reuters. "I wish these walls would be lifted, but the suffering we went through was horrible. No one wants to go through that again."

Once-towering blast walls put up at the height of Iraq's sectarian bloodshed are coming down and letting light into dusty city streets, or connecting divided neighbourhoods, for the first time in three or more years.

Violence has dropped sharply across Iraq in recent months: the removal of the walls is prompting dreams of a boom in business as restaurants and shops once again emerge in sunlight.

But there is also fear.

Abu Ali's 17-year-old son was one of at least 140 killed in Baghdad's single most devastating insurgent attack since the 2003 U.S. invasion: a truck bomb primed by suspected al Qaeda militants which blew up in the Sadriya market area on April 18, 2007.

Insurgents including Sunni Islamist al Qaeda continue to launch car and suicide bombings aimed at unsettling Prime Minister Nuri al-Maliki's majority Shi'ite Muslim-led administration and tipping the country back into sectarian war.

There are fears that militants will try to stoke tensions further ahead of a parliamentary election next January -- a vote that will test whether Iraq's feuding factions can live in peace after years of turmoil -- and also as U.S. combat troops pull out of city centres this month.

CONCRETE RAVINES

The blast walls turned Baghdad and other cities into warrens of concrete ravines with here and there, scorch marks from explosions. Some became a tableau for impromptu urban art or billboards for political posters.

The concrete slabs weigh five tonnes each and are meant to absorb the worst of the impact of any bomb blasts.

Watching workers take them down, Abbas Fadhil, a 31-year-old who owns a restaurant alongside the government ministries and foreign embassies of the capital's heavily fortified Green Zone, said he was happy and scared at the same time.

"I'm happy because this will be positive for my business, and I'm scared as opening it up it may encourage terrorists to attack the area," he said. "It could be an easy target."

In the Green Zone, off-limits to most Iraqis, many of the 4- meter slabs ringing official buildings will remain. But routes through it are due to be opened up, easing traffic pressures that cause hours of gridlock in neighbouring streets.

Back in Sadriya, on the opposite bank of the River Tigris, an Iraqi army officer said he knew the locals hated the walls.

"But they were erected for their safety. There are many terrorist sleeper cells waiting to grasp any opportunity to attack," he said. "Removing them is not only a strategic mistake but it is a matter of gambling. It is completely risky."

"DARING DECISION"

The government says opening closed streets and removing the walls is almost universally popular. A survey earlier this year by the state-run National Media Centre found backing for the move from nearly 90 percent of those asked.

As well as restricting movement and causing congestion, the walls have curbed services like garbage collection and projects including a $100 million sewage renovation for Sadr City -- a large Shi'ite slum where the authorities want to win friends.

"We need a revolution. We need to take the daring decision to remove all the concrete walls, especially where they isolate whole districts," Baghdad Mayor Saber al-Issawi told Reuters.

"There are hundreds of thousands, maybe even a million, in Baghdad ... In a simple calculation, we are losing billions of dinars every year because of the existence of the walls."

A municipal council spokesman said the walls disfigured one of the world's oldest cities, and that the opening of roads and bridges over the Tigris showed life returning to normal.

"We want Baghdad to be bright and flourishing and to amaze visitors in a way that befits its cultural history and its present," said the spokesman, Hakim Abdul Zahra.

He said the tonnes of dismantled concrete slabs were being trucked to military sites for use by the security forces.

Market trader Khalid Obaid, 42, said he felt a huge weight had been lifted from his chest as he watched the crews at work.

"We want to see people. We haven't seen many since this area was locked down," Obaid said. "My wife cried with happiness when she saw the cranes lifting the walls off the streets." (Additional reporting by Waleed Ibrahim; Writing by Daniel Wallis; Editing by Sara Ledwith)

By Aseel Kami and Khalid al-Ansary