In this sense, they mean the same thing. Consider them to be synonyms.

As nouns Strike means causing severe damage while attack means applying a violent force.

"Strike" is a more neutral or formal word than "attack". Saying that a country "strikes" another would be considered more neutral (not in favor of either side. Stating plain fact) and professional than saying that the country has "attacked" another. In general use, strike implies a single action against (a single blow, one bombing, one excursion to raid a place, ect.), while an attack might describe one offensive action, or a short campaign (Ex. "the attack on this city began with strategic raids, followed by a push towards the city center and parties sent in to place bombs and traps for the enemy).

In my opinion the word choice here is based on politics. The word 'attack' has a negative connotation; people who attack others are bad. The word 'strike' is more positive: it is percieved as a strong, positive and necessary thing. (I'm not discussing the politics of the situation; ONLY the implications of the words.)