The Taliban announced the start of their spring offensive on Tuesday, pledging to launch large-scale offensives against government strongholds backed by suicide and guerrilla attacks to drive Afghanistan's Western-backed government from power.

The announcement of the formal start of "Operation Omari," named after the late Taliban founder Mullah Mohammad Omar, comes just days after Secretary of State John Kerry visited Kabul and reaffirmed U.S. support for the national unity government led by President Ashraf Ghani.

"Jihad against the aggressive and usurping infidel army is a holy obligation upon our necks and our only recourse for reestablishing an Islamic system and regaining our independence," the Taliban said in a statement.

The insurgency has gained in strength since the withdrawal of international troops from combat at the end of 2014 and the Taliban are stronger than at any point since they were driven from power by U.S.-backed forces in 2001.

The operation will include assassinations of enemy commanders in urban centers, the Taliban statement said. In line with recent statements, it also said it would establish good governance in areas it controlled as well as avoiding civilian casualties and damage to infrastructure.