By Isabel Coles and Ned Parker
ARBIL Iraq (Reuters) - Western countries will end up fighting insurgents who have overrun large parts of Iraq on their own doorstep unless they intervene to combat the threat at its source, a senior Kurdish security official said in an interview.
Masrour Barzani, head of the Kurdish region's National Security Council, said he doubted Iraq's army would be able to roll back militant gains without help from outside, but that the world did not appear serious about confronting the insurgency.
Iraq's million-strong army, trained and equipped by the United States at a cost of around $25 billion, largely evaporated in the north after militants from the Islamic State overran the city of Mosul last month.
From there, they went on to seize most Sunni majority areas with little resistance, putting Iraq's very survival as a unified state in jeopardy as politicians wrangle in Baghdad over forming a government.
Barzani said Kurdistan, which has managed so far to insulate itself against violence in the rest of Iraq and neighbouring Syria, was the "frontline against terrorism" in the Middle East, and that the inaction of Western nations was at their peril.
"They have a choice: either they can come and face them here, or they can wait for them to go back to their own countries and face terrorism on their doorsteps," he told Reuters in an interview on Saturday.
The Kurds, who have their own armed forces known as the "peshmerga", now share all but 15 kilometres (10 miles) of their southern border with insurgents who have declared an Islamic caliphate across Iraq and Syria.
For now, the militants are busy fighting what remains of the Iraqi army backed by Shi'ite militias further south, but they may eventually turn to the north, where the Kurds have expanded their territory by as much as 40 percent.
The peshmerga have already clashed with insurgents, who are now armed with weapons seized from the Iraqi army, many of them supplied by the United States, which has urged the Kurds to take on the Islamic State, formerly known as ISIL or ISIS.
"ISIS now has a lot of modern military equipment in their possession, and to fight against them I think the peshmerga have to be much better equipped than they are," Barzani said. "For that, the United States and the international community as a whole should feel responsible".
"We have had talks with the United States, with some of the European countries, but no practical steps have been taken to provide assistance to the KRG (Kurdistan Regional Government), especially on the military front".
"GREAT CONCERN"
Barzani put the number of Islamic State militants who took over Mosul on June 10 at fewer than 2,000, but said new recruits, fighters from Syria and capitulation of other armed factions had increased that to as many as 12,000. Another estimate by a security official in Baghdad puts the size of IS at more than 20,000 after the fall of Mosul. But there is no way to independently verify the numbers.
Many tribal and insurgent groups have made common cause with the Islamic State to fight against Shi'ite Islamist Prime Minister Nuri al-Maliki, but there are tensions within their ranks that have already led to infighting.
Assessing the strength of those groups relative to the Islamic State (IS), Barzani said they were "much weaker". He suggested the KRG would be prepared to work with "moderate" tribes and forces protecting their own areas from IS.
Iraqi Kurdistan has cultivated an image of relative stability in a turbulent neighbourhood, although a bombing of the headquarters of the security services in the regional capital Arbil last September showed the region remained a target.
Barzani said Kurdish security services had managed to thwart "quite a few" attacks since then, and that the influx of hundreds of thousands of Iraqis displaced from other parts of the country into Kurdistan posed an added challenge.
"It makes the job of our security forces much more difficult to try to keep an eye and monitor the situation," Barzani said. "We are trying our best to make sure there are no sleeper cells activated".
(Writing by Isabel Coles; editing by Tom Pfeiffer)