Donald Trump`s anti-Muslim rhetoric undermines US national security by boosting the Islamic State (IS) group, the Pentagon has warned.The leading Republican presidential candidate has said Muslims should be banned from entering the US, in the wake of the deadly California attacks.But Pentagon press secretary Peter Cook said such talk ‘bolsters Isil`s narrative’, referring to IS. There has been a global outcry since Trump made his remarks.US Secretary of State John Kerry joined the onslaught of condemnation on Tuesday afternoon when he said they were ‘not constructive’ in the fight against IS.The IS militants are the target of a US-led bombing campaign in Syria and Iraq. Trump announced his plan days after an attack in California raised US fears about homegrown terrorism.A Muslim couple, believed to have been radicalized, opened fire and killed 14 people at a health centre in San Bernardino.One of the two perpetrators, Tashfeen Malik, reportedly pledged allegiance to Islamic State on the day of the tragedy.But responding to Trump`s remarks, the US Pentagon said a border closed to Muslims would harm American efforts to counter extremist ideology. Without mentioning Trump by name, Cook said: ‘Anything that bolsters Isil`s narrative and pits the United States against the Muslim faith is certainly not only contrary to our values but contrary to our national security.’