* Bombs kill 10 in volatile Helmand province
* Officials lower death toll of incident to five from 21
* Violence increasing ahead of elections
(Updates after death toll lowered in attack)
By Ismail Sameem
KANDAHAR, Afghanistan, Aug 6 Two roadside bombs in Afghanistan's most violent province killed five revellers heading to a wedding and five policemen, officials said on Thursday.
The first bomb struck a family heading to a wedding in a tractor on Wednesday in volatile Helmand province's Garmsir district, where a new force of U.S. Marines has been battling Taliban guerrillas since launching a major operation last month.
Earlier on Thursday Afghanistan's Interior and Defence ministries had put the toll from the wedding attack at 21 dead. But officials lowered the toll to five after investigating further, Helmand police chief Asadullah Sherzad said.
"Because of the remoteness of the area we did not have accurate information in the morning. The toll of five killed and five wounded is precise information and that comes from an investigation by our team," he told Reuters by telephone.
The second bomb exploded near a police vehicle on Thursday in Naad Ali district, also in Helmand, killing five policemen and injuring three.
Violence, already at its worst since the Taliban were ousted in 2001, has increased in the last weeks of campaigning for an Aug. 20 presidential election, which militants vow to disrupt.
Thousands of U.S. Marines and British troops last month simultaneously launched the war's two biggest operations in separate parts of Helmand to seize territory from Taliban fighters ahead of the election.
The ongoing operations are meant to expand the government's control of the volatile south ahead of the election, part of U.S. President Barack Obama's new strategy to defeat militants, which has seen him send tens of thousands of extra troops.
Homemade bombs are by far the insurgents' deadliest weapon, and they have also mounted suicide strikes on provincial government buildings in recent months throughout the south and east. On Tuesday they struck the capital Kabul with rockets.
An Afghan government map obtained by Reuters shows that almost half of Afghanistan is at a high risk of attack by the Taliban and other insurgents, with 13 of its 356 districts coloured dark red, marking them under "enemy control".
At least 71 international troops were killed in July, by far the worst monthly toll for foreign forces since the war started.
In Kandahar province, which borders on Helmand, NATO-led forces fired on a vehicle from a helicopter late on Wednesday, but disputed Afghan officials' accounts they killed civilians.
Jirai district governor Niaz Mohammad Sarhadi said five people were killed in a vehicle carrying cucumbers. But U.S. military spokeswoman Lieutenant Commander Christine Sidenstricker said the vehicle was being loaded with weapons.
"Our information is that insurgents have been killed."
The U.S. military also reported the death of a service member in the western province of Farah while on patrol on Wednesday. (Additional reporting by Golnar Motevalli, Jonathon Burch and Sayed Salahuddin in Kabul; writing by Peter Graff and Golnar Motevalli; Editing by Jon Hemming)