The United States is to deploy more troops and heavy tanks in South Korea as part of a military rebalance at a time of raised tensions on the Korean peninsula.

Forty M1A2 Abrams main battle tanks, 800 soldiers and 40 Bradley fighting vehicles from the 1st US Cavalry Division will be sent on deployment in February, the Pentagon announced on Wednesday.

South Korea's Yonhap news agency quoted military officials as saying that the new troops and materiel would be deployed in North Gyeonggi Province, just south of the demilitarized zone separating the two Koreas.

The deployment comes at a time of raised tensions on the peninsula after the North's young leader, Kim Jong-Un, executed his powerful uncle last month, the biggest upheaval inside the ruling dynasty for years.

The North under Jong-Un has continued to develop nuclear weapons and test missiles in defiance of UN resolutions.

Commenting on the deployment, John Kerry, the US secretary of state, said: "The United States and the Republic of Korea stand very firmly united, without an inch of daylight between us, not a sliver of daylight, on the subject of opposition to North Korea's destabilising nuclear and ballistic missile programmes and proliferation activities.

Army Colonel Steve Warren said: "This addition is part of the rebalance to the Pacific. It's been long planned and is part of our enduring commitment to security on the Korean peninsula. 

"This gives the commanders in Korea an additional capacity: two companies of tanks, two companies of Bradleys."

The US has 28,000 troops based in South Korea, which has remained technically at war with Communist North Korea since the 1950-1953 Korean conflict ended in stalemate.

A Pentagon spokesman said the additional equipment would be left behind after the nine-month deployment to be used by follow-on rotations of US forces.

Barack Obama, the US president, announced a strategic rebalancing of priorities toward the Pacific in late 2011 while winding down US commitments in Iraq and Afghanistan.