Assyrian leaders in Iraq have lambasted Isis militants who bulldozed the ancient city of Nimrud, accusing them of trying to "uproot" their beleaguered community. Isis fighters used bulldozers to smash and pillage the remains of the city on Thursday, according to local archaeologists and the Iraqi government, in an act of cultural vandalism that the UN's cultural agency declared a "war crime". "This is very hard for us. We feel Isis is destroying our civilisation and trying to uproot us from this area," said Kaldo Oghanna, an official with the Assyrian Democratic Movement. Assyrians make up most of the Christians in Iraq, who numbered some 1.6 million before 2003, said Mr Oghanna, but that figure has now fallen below 400,000 as the minority group suffers attacks against their community. In July Isis gave the Christians of Mosul an ultimatum to pay a tax, convert to Islam or die by the sword, most fled. The destruction of the ancient Assyrian city of Nimrud, which lies on the Tigris River 20 miles south of Mosul follows a video released by Isis last week showing fighters hammering statues dating from the end of the 8th century BC in Mosul. The Independent reported warnings by fighters that Nimrud would be their next target for destruction. Mr Oghanna said that Isis sent heavy machinery into Nimrud because some of the large winged bull and lion statues known as "Lamassu" could not be destroyed with normal tools. Irina Bokova, director general of the UN's cultural agency, Unesco, said in a statement that Nimrud's destruction represented a war crime, and was "yet another attack against the Iraqi people, reminding us that nothing is safe from the cultural cleansing under way in the country". "I call on all political and religious leaders in the region to stand up and remind everyone that there is absolutely no political or religious justification for the destruction of humanity's cultural heritage," she said. An eye witness told The Independent that Isis bulldozers arrived at the historic site, which for the militants represents idolatry, on Thursday and began destroying and looting treasures. The scale of the destruction is not yet clear. An Iraqi archaeologist from Mosul who fled when the militants took control of the city last summer spoke of her shock at the irreparable cultural damage. "Within the palaces there are reliefs showing scenes of the life of monarchy and some of the achievements of kings that we believe were stolen or destroyed," she said. The city of Nimrud dates from around the 13 century BC, according to archaeologists, and was built to show off the might of the neo-Assyrian empire. Nimrud, which was the capital of the empire for 400 years, contained royal palaces. Dr Katharyn Hanson, a fellow at the University of Pennsylvania and specialist in Mesopotamian archaeology, said that the destruction represented a "heavy blow for Iraqi archaeologists and for humanity's collective past". Mr Oghanna also acts as the spokesperson for the newly formed Christian militia called the Nineveh Plain Protection Units. He said his fighters are training to protect their areas but that more international support to defeat Isis is needed. "We are appealing to the international community and we are demanding that the government in Iraq cleanses these areas of Isis as soon as possible because they will destroy everything, we need to do what we can now to stop these people invading our civilisation."