London: The recent airstrikes by the United States in the western Iraqi city of Ramadi have killed around 350 Islamic State of Iraq and the Levant (ISIS) resulting in the loss of almost half of their defending force.

According to the Guardian, Colonel Steve Warren, spokesman for the US military command in Baghdad, told reporters at the Pentagon that around 600 to 1,000 ISIS fighters had been inside Ramadi.

But US officials remain reluctant to predict how long it will take to reclaim the city which is crucial to the Iraqi government's hopes of restoring its borders.

Speaking about Iraqi progress in retaking Ramadi, Defense secretary Ash Carter said that the process has been 'disappointingly slow'. Warren also announced that the US airstrikes in late November killed three senior ISIS leaders, including Abu Salah, who was allegedly the group's financial minister.

'Killing him and his predecessors exhausts the knowledge and talent needed to coordinate funding within the organization,' Warren said. He added that the three were killed in airstrikes near the northern Iraqi town of Tal Afar.