Does the Monk's Flurry of Blows trigger mark retribution?

Question

Scenario:

• Monk is marked by Fighter.
• Monk attacks Fighter.
• Monk uses Flurry of Blows on a different creature.

Does the Fighter get to use Combat Challenge to attack the Monk?

UPDATE: I found this thread that argues that FoB is an attack. Whether or not that argument is correct, this suggests at least three possible paths of reasoning for this question that I'd like to explore; in particular, the third one:

1. Flurry of Blows is an attack and triggers mark retaliation. (argument: it has a target and deals damage, like post-errata magic missile)
2. Flurry of Blows is not an attack and does not trigger mark retaliation. (argument: it doesn't have an attack roll)
3. Flurry of Blows is part of the same attack and does not trigger mark retaliation. (argument: it is like hunter's quarry, warlock's curse, or rogue's sneak attack)

Answer 1

Yes

Per the Rules Compendium, p89-90:

Power Types: There are two types of powers.

Attack Powers: These powers are used to damage or hinder others. ...

Utility Powers: These powers have a variety of uses. ...

A power's type is usually relevant only when a character uses a feat or some other game feature that works with powers of one type or the other. If a power's type isn't stated, the power is an attack power if it includes an attack roll or if it deals damage. Otherwise it is a utility power.

Flurry of Blows does not have a type listed (rather, it's listed as "Monk Feature" which is not a type) and it deals damage, therefore it is an attack.

The one counter-argument I can think of would be to say that Flurry of Blows is not an attack because an attack is a type of power, and Flurry of Blows is not actually a power. There are several class features that are never described as powers in the books (hunter's quarry for example) but that the Character Builder creates power cards for simply because a power card is an easy way to keep track of the ability; despite having power cards, these abilities are not actually powers. This does not apply in the case of Flurry of Blows, however; both variants in PHB3 have power cards in the printed book, and the actual class feature says:

You gain the (centered / stone fist) flurry of blows power.

Answer 2

IMPORTANT NOTE: This answer is preserved at the asker's request. This was my interpretation until I noticed p90 of the RC. I no longer believe it is correct.

No

Flurry of Blows is not an attack (see PHB3 p65; neither FoB power has an attack roll, and the power type is "Monk Feature" rather than "Monk Attack"). There are a wide number of class, epic destiny, and especially paragon path features that deal damage without an attack roll that are pretty clearly not "attacks" from a rules standpoint, as well as some utility powers, which are by definition not "attacks"; thus, while Flurry of Blows certainly seems like an attack in the fluff sense, it is not an attack in terms of the game rules.

Marks are only triggered by attacks that do not include the creature that marked the attacker. The definition of the marked status on p277 of PHB1 says,

Marked: You take a -2 penalty to attack rolls for any attack that doesn't target the creature that marked you.

No mention of affecting powers that deal damage without an attack roll, which is what Flurry of Blows does. Nor does the fighter's Combat Challenge trigger; from PHB1 p76:

Combat Challenge: ... In addition, whenever a marked enemy that is adjacent to you shifts or makes an attack that does not include you, you can make a melee basic attack against that enemy as an immediate interrupt.

Again, no mention of powers that deal damage without an attack roll.

TLDR: Marks and mark punishment are triggered by attacks, and Flurry of Blows is not an attack because it has no attack roll.