WASHINGTON, Oct 10 (Reuters) - Washington's push on Pakistan to get tough on militants on its territory is prompted by worries about an attack on U.S. soil, a concern the United States will press in talks with Islamabad later this month. A U.S. official last week countered suggestions that the tougher approach is driven by the need to show progress ahead of the Oct. 22 talks by an Obama administration strategy review of the war in Afghanistan in December. The failed Times Square bombing in May and the recent terrorism alert for Europe fueled fears of an attack, prompting the stepped up drone attacks in Pakistan's rugged northwest and pointed U.S. comments pressing Islamabad's to pursue militants more aggressively. "There is really mounting concern that we are extremely vulnerable to an attack from a group in Pakistan that could occur," the U.S. official said, speaking on condition of anonymity. Such an attack would trigger a critical change in ties with Islamabad, the official warned. "(An attack) will change the nature of the relationship, not because necessarily it makes sense to, but because the congressional outcry and the public outcry will be such that you will have to dramatically do things quite differently," the official added.