The cost of an Air Force program to replace aging nuclear missiles has ballooned to about $160 billion from $95.8 billion, three people familiar with the matter said, threatening to slash funding for other key modernization plans.

The new project, named the Sentinel intercontinental ballistic missile (ICBM) program, is designed and managed by the Virginia-based leading provider of manned air systems, Northrop Grumman Corp.

A Pentagon program to replace some of its aging intercontinental ballistic missiles will be years behind schedule and 81% over budget, the US military said on Monday. The project, now named the Sentinel intercontinental ballistic missile program, is designed and managed by Northrop Grumman, and aims to replace aging Minuteman III missiles.