BRUSSELS — The Obama administration pressed its allies on Wednesday to follow through on their pledges to Afghanistan’s security after most international troops withdraw in 2014, fearful of being left with the check in an era of austerity budgets and cutbacks.

At a summit in May, donors pledged $4.1 billion a year to support Afghan forces from 2015 to 2017, firming up a key plank of the US strategy to leave behind a secure Afghanistan. But many governments have yet to come up with the cash.