UPDATE 1-Bahraini teenager killed in clash with police

* Conflicting accounts of youth's death circulate

* Comes as U.S. says worried about jailing of activist

* Shi'ite Muslim majority says marginalised, govt denies

DUBAI, Aug 18 (Reuters) - A 16-year-old protester was killed

after what opposition activists in Bahrain said was a "brutal

attack" by security forces, but which the Bahrain government

described as a defensive response to a petrol bomb attack on

police.

The opposition says more than 45 people have been killed in

protests since June 2011, when the government lifted martial law

it had imposed to help quash pro-democracy demonstrations by its

Shi'ite Muslim majority inspired by revolts against repressive

dynasties across the Arab world.

However, the Interior Ministry says protesters have injured

more than 700 police officers in clashes and that the police,

who do not use live fire, have been exercising restraint.

The protester's death - after a demonstration on Friday

night - came as the United States, an ally of Manama, expressed

concern over Bahrain's jailing of a prominent opposition

activist, Nabeel Rajab, for three years.

The government identified the dead youth as 16-year-old

Hussam al-Haddad, and said he had been among protesters throwing

petrol bombs at police and had died after being taken to

hospital.

The opposition Bahrain Centre for Human Rights said

witnesses had seen the security forces fire birdshot at Haddad

before men in plainclothes kicked him repeatedly as he lay on

the ground while police stood by.

The main opposition Wefaq movement said in a statement in

Arabic that Haddad had been "martyred after being brutally

attacked" and activists posted what they said were pictures of

his body, apparently severely bruised and marked by dozens of

birdshot wounds.

Reuters was unable to verify the pictures independently.

The government said police were acting in self defence.

"Terrorists launched petrol bombs at close range, forcing

the police to take the necessary actions to defend themselves

and innocent bystanders from the potentially lethal attack," the

Information Affairs Authority said in an emailed statement in

English.

"Despite warning shots by the police the attack continued;

so security personnel dealt with the case according to its legal

authority," it added, citing the police chief of the Muharraq

district where the incident took place.

Hundreds of people marched peacefully through the Muharraq

district for Haddad's funeral on Saturday, witnesses said.

Rights groups have accused the government of firing teargas

canisters at close range and into confined spaces as a weapon

instead of using the gas solely to disperse protests, something

the government has denied.

OPPOSITION DEMANDS

Bahrain's own inquiry into the overall uprising and

subsequent violence said at least five people had died under

torture in government custody and recommended quashing verdicts

issued against protesters by a military court.

On Wednesday, the country's top appeals court reduced

sentences handed down to 11 people accused of attacking a

soldier during the turmoil.

Bahrain's Shi'ites say they have been marginalised in the

tiny island kingdom's political and economic life, but the

Sunni-led government denies this.

The ruling family has rejected the main opposition demand

for an elected parliament with full powers to pass laws and form

governments, but has enacted reforms to increase parliamentary

scrutiny over ministers and has said it will reform the police.

On Tuesday, King Hamad bin Isa Al Khalifa said the country's

problems were caused by "foreign plots", restating the

government's accusation that the uprising was instigated by

Shi'ite Iran, something that both Tehran and protesters deny.

However, he added that the government was "sparing no effort

to solve" its internal problems and that Bahrain had become a

country of democracy and human rights.

Wefaq said the speech showed Bahrain's government was not

coming under pressure from Washington to hold talks with the

opposition.

The U.S. Fifth Fleet is based in Bahrain, on the west of the

Gulf, a transshipment route for 40 percent of the world's

seaborne oil exports which is bordered to the north by Iran.

On Friday, the U.S. State Department said it was "deeply

concerned" by the jailing of Rajab, a prominent opposition

leader, on charges of leading illegal gatherings.

"We have repeatedly urged the government of Bahrain to take

steps to build confidence across Bahraini society, and to begin

a meaningful dialogue with the political opposition and civil

society. Excessive punishment for peaceful expression ... will

not contribute to those efforts," it said in a statement.

Bahraini Information Minister Samira Rajab said on Saturday

that the activist had been tried fairly and had enjoyed full

access to legal aid.