(Recasts with new suicide attack)

By Hamid Shalizi

KABUL, Sept 11 (Reuters) - Two suicide bombers struck in two Afghan provinces in the south on Thursday, killing four people and wounding 14, officials said, the latest attacks in worsening violence in the country.

The al Qaeda-backed Taliban have stepped up their campaign of suicide attacks and roadside bombs this year as part of their attempts to topple the Afghan government and eject the foreign troops who support it.

One of the bombers blew himself up near a U.S. security firm convoy in the southern Afghan province of Kandahar killing two civilians and wounding six.

"The suicide bomber was identified and we shot at him before he could ram his car into the convoy," provincial governor spokesman Zulmai Ayubi said.

Another attacked a police vehicle in Nimroz province, killing a policeman and a civilian and wounding eight passers-by, the provincial governor Ghulam Dastagir Azad said.

He said the bombing was the 15th attack this year on coalition and Afghan forces.

SECURITY TIGHT

Security was tight in some parts of Afghanistan on the seventh anniversary of the Sept. 11 attacks.

Seven people were wounded when a bomb attached to a bicycle exploded near the governor's office in Ghazni province, southeast of Kabul.

Violence in Afghanistan is at its highest level since the Taliban were ousted in 2001. More than 2,700 people have been killed this year, including 1,100 civilians, aid agencies say.

Earlier the U.S. military said U.S.-led forces targeted Taliban fighters in eastern and southeast Afghanistan, including veteran commander Jalaluddin Haqqani's network, killing several militants.

Haqqani is considered close to Osama bin Laden, the fugitive al Qaeda chief blamed for the Sept. 11, 2001, attacks on the United States.

The raids came days after U.S. drones fired missiles into Pakistan's tribal area, killing 23 people, mostly relatives of Haqqani who was once backed by the United States during the war against the Soviet invasion and occupation.

U.S.-led coalition forces targeted a Haqqani sub-commander who had been directing roadside bomb attacks in Khost province near the border with Pakistan. One militant was held in the operation on Wednesday, the coalition said in a statement.

Also on Wednesday, fighting erupted in Ghazni province during a coalition operation against a militant helping foreign fighters enter Afghanistan. Several insurgents were killed, the U.S. military said.

A roadside bomb killed a British soldier from the NATO-led force in southern Afghanistan on Wednesday, the alliance said. (Writing by Sanjeev Miglani) (Kabul newsroom +93 707 924 923))

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