With the escalating Ukrainian crisis towards the top of the agenda at this week’s NATO summit in Wales, a group of former American intelligence workers is urging the alliance to be careful before crafting a response.

Sixty foreign leaders and dozens of diplomats and defense officials from around the globe will convene at the event this week and are expected to approve a plan that calls for assembling a 4,000-strong “spearhead” force to counter “Russia’s aggressive behavior,” NATO Secretary-General Anders Fogh Rasmussen said on Monday, in the wake of the release of satellite images purported to show the advancement of at least 1,000 Russian troops and artillery into eastern Ukraine.