The city of Ramadi could be taken back from Islamic State of Iraq and Syria (ISIS) militants “in days,” Iraqi PM Haider al-Abadi said in an interview with the BBC on Monday.

Abadi made the remarks amid an Iraqi army offensive to counterattack ISIS militants who seized the city last week.

“It makes my heart bleed because we lost Ramadi, but I can assure you we can bring it back soon,” he said. The prime minister added that his forces were thrown by ISIS shock tactics.

“They have the will to fight but when they are faced with an onslaught by Daesh [ISIS] from nowhere… with armored trucks packed with explosives, the effect of them is like a small nuclear bomb – it gives a very very bad effect on our forces,” he said.

Abadi said Iraq needed more international support as many ISIS fighters were slipping into Iraq from Syria.

“Not controlling Syria-Iraq border more closely was an error. Syria is in chaos which made IS become stronger. We’ve asked our international coalition partners to tighten control over the border,” he said.

On Sunday, ISIS seized the Iraqi side of a key border crossing with Syria after isolated government forces pulled out, a police officer and a provincial official said, according to Agence France-Presse.

“Some observers say IS now controls 50 percent of Syria’s entire territory – as well as a third of Iraq,” the BBC reports, using an alternative acronym for ISIS.

U.S. Defence Secretary Ashton Carter told CNN on Sunday that the seizure of Ramadi showed Iraqi troops lacked the will to fight.

Carter said the Iraqis had chosen to withdraw despite the fact that they “vastly outnumbered” ISIS militants.

In response to the remarks, Abadi told the BBC: “[Mr Carter] was very supportive of Iraq and I am sure he was fed with the wrong information.”