BAGHDAD, April 15 (Reuters) - When insurgents blew up the Sarafiya Bridge in Baghdad, a piece of Yaseen Kathim's past was sent forever crashing into the muddy waters of the Tigris River.

"When I heard it was destroyed, I felt I was hit. It was my bridge. I used it everyday," said Kathim, a 37-year-old doctor, lamenting the destruction last Thursday of the steel span.

But the bombing of one of Baghdad's most enduring symbols was not only an attack on the city's infrastructure. Some residents and officials fear it could be part of a more sinister plot by insurgents to split Baghdad, with a Shi'ite east bank and a Sunni west bank.

On Saturday, a ѕυιcιdє car bomber blew himself up at a ramp leading to the Jadriyah bridge, causing no structural damage.

It is unclear if the two attacks were related, but the U.S. military said insurgents appear to be changing tactics.

"The constant strategy of the terrorists is to look at ways to divide and create terror and make life difficult for the people of Iraq," Rear Admiral Mark Fox, a spokesman for the U.S. military in Iraq told reporters on Sunday, adding military planners were "studying carefully" the two incidents.

"The terrorists are planning to split Karkh from Rusafa," said a senior Shi'ite lawmaker, using Baghdad's ancient names for the west bank (Karkh) and the east bank (Rusafa).

"This has been the plan by terrorists and their political allies all along to try and drive Shi'ites out of Karkh so they can split Baghdad in half."

On the other side of the sectarian divide, parliament speaker Mahmoud Mashhadani, an outspoken Sunni politician, called the destruction of Sarafiya a "conspiracy to isolate the two halves of Baghdad".

BAGHDAD'S "BRIDGE WARS"

Baghdad, a city of 7 million, has been religiously mixed for most of its history since it was founded some 1,200 years ago on the banks of the Tigris River by Abbasid Caliph al Mansour.

Its dozen bridges linking the east side with the west side were once a symbol of Baghdad's diversity, where Shi'ites, Sunni Arabs, ethnic Kurds and Christians lived together.

But since the bombing of a Shi'ite shrine in Samarra in February 2006, a wave of communal violence has reshaped the city's fabric, carving out sectarian fiefdoms. Sunnis now mainly live on the west side of the river and Shi'ites on the east.

Some talk gloomily of Baghdad's "bridge wars". Although the Sarafiya Bridge was built in the 1940s by the British, its destruction prompted eulogies in local newspapers, as if it was a repeat of the shelling of the fabled Mostar bridge, which became a worldwide symbol of Bosnia's 1992-95 cινιℓ ωαr.

Saad Eskander, director of Iraq's National Library and a historian, said blowing up Baghdad's bridges has been a military strategy to conquer and defend the city since ancient times.

Medieval rulers burnt Baghdad's bridges, then wooden planks laid over boats roped together, to stop invading Mongols from sacking the city. The U.S. military, in its wars against Saddam Hussein, destroyed bridges in Baghdad to hinder troop movements.

"Destroying the Sarafiya bridge is an attempt to break Iraq's unity and to polarise our society," Eskander said.

"It is a message that Baghdad will soon become two Baghdads -- one for the Shi'ites and one for the Sunnis."

But for those who share childhood memories of swimming under the 453 metre (l,485 feet) long span as trains chugged along its railway tracks above, Baghdad bridges will never be severed.

"If they think they can split Karkh from Rusafa they are dreaming," said Saadi Ahmed, who runs a money exchange store.

"The terrorists are trying to destroy Baghdad's landmarks to erase our proud history of civilisation." (Additional reporting by Wathiq Ibrahim)