(PTI): The bulk of the extra 17,000 US troops will be deployed in Afghanistan by mid-July as Washington strives to tighten its grip on the region.

“10,000 marines are beginning to arrive now and will continue to arrive for the next month and a half or so and they will be principally located in Helmand but also in Farah,” Colonel Greg Julian, spokesman for US forces told Reuters on Sunday.

He added that some 7,000 US army troops along with “additional helicopters” will also be deployed to the mainly “rural areas” of southern Kandahar province by the set date.

Julian said that a further 4,000 troops will also be sent to the south and west of the war-torn country by August, mainly to train Afghan security forces.

Despite the growing presence of foreign troops in the southern Helmand province and the western Farah district, the area is considered as a haven for insurgents, where many NATO alliance troops deployed in the country, have met their deaths.

The Obama White House says that the 21,000 additional troops are to reinforce security ahead of the August 20 presidential elections, and are to support the NATO-led troops which have struggled to fight an escalating insurgency there.

The surge in US troops in Afghanistan comes amid frosty relations between Kabul and Washington, over the US bombing of civilians about a month ago.

The raid which left some 150 people including 95 children dead is dubbed as the deadliest incident for Afghan civilians since the 2001 US-led invasion.

Human rights and medical officials have also accused the US forces of using white phosphorus during the lethal strikes.

Pentagon Chief Robert Gates, meanwhile, has said that an influx of more than 21,000 US troops would not reduce the demand for airstrikes across the conflict-torn country.