Islamic State" (IS) claimed responsibility for the attacks in Paris on Friday 13th November - Reuters 14th November. At the time, the President of France described the attacks as "an act of war."
The United Nations Security Council has now adopted UN Security Council Resolution (UNSCR) 2249 (2015) - Read the Resolution. The resolution calls upon (but does not mandate) those Member States with the capacity to do so to take
Resolution 2249 begins by recalling a number of other resolutions including Resolution 2199 (2015) which underlined the obligations of Member States to take steps to prevent terrorist groups in Iraq and Syria from benefiting from trade in oil, antiquities and hostages, and from receiving donations. UNSCR 2199 was passed under Chapter VII of the UN Charter. Further resolutions under Chapter VII are UNSCRs 2213 and 2214 (2015). 2213 called for an immediate and unconditional ceasefire and extended the United Nations Support Mission there (UNSMIL) until 15 September, and 2214, adjusted the arms embargo on the country in light of the terrorist threat there.
The exact action to be taken under UNSCR 2249 remains to be seen but the Council has now given its authority to all necessary measures though it will be noted that the Council requires the measures taken to be " in compliance with international law, in particular with the United Nations Charter, as well as international human rights, refugee and humanitarian law." The word "necessary" is also important.
The security council decided to "remain seized of the matter.”
Difficulties with Resolution 2249
Resolution 2249 is not as simple as it may appear at first sight and it is certainly not a resolution specifically passed under Article 42 of Chapter VII of the UN Charter. Regrettably, it appears to contain difficulties as to what precisely it authorises. For further discussion of this see European Journal of International Law - The constructive ambiguity of the Security Council's ISIS resolution
where it is argued that:
"..... the Council does not authorize “all necessary measures,” nor does it decide that they be taken, but rather “calls upon” states to take such measures. This difference in language itself suggests that though the Council contemplates, and perhaps would even welcome, the use of force by states, it does not authorize such action....."
Against that view, it is arguable that the resolution permits the use of force by those nations that choose to use it for the objectives specified in the resolution but it does not require any nation to actually take action or to use force if doing so. For one opinion along these lines see Brian Barder's blog.
Barder states - " ..... It is difficult to see how UN member states responding to the Security Council’s call could try to “prevent and suppress terrorist acts” by ISIL on territory that it controls, or in particular “to eradicate the safe haven [ISIL] have established over significant parts of Iraq and Syria” without using military force. And it’s even more difficult to imagine how activity expressly encouraged by the Security Council in a formal and unanimous resolution could be deemed to be illegal or unauthorised."
Article 41 of the Chapter VII permits the Security Council to take action not involving armed force. Article 42 of the Charter goes on to state:
Should the Security Council consider that measures provided for in Article 41 would be inadequate or have proved to be inadequate, it may take such action by air, sea, or land forces as may be necessary to maintain or restore international peace and security. Such action may include demonstrations, blockade, and other operations by air, sea, or land forces of Members of the United Nations.
Sir Michael Wood on the Interpretation of UN Security Council Resolutions
The United Nations Act 1946 permits Orders in Council to be made to give effect to UN Security Council measures not involving the use of armed force.
It is worth noting another development which took place prior to the Security Council resolution.
The North Atlantic Treaty Organisation (NATO) Charter (Article 5) states:
"The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and consequently they agree that, if such an armed attack occurs, each of them, in exercise of the right of individual or collective self-defence recognised by Article 51 of the Charter of the United Nations, will assist the Party or Parties so attacked by taking forthwith, individually and in concert with the other Parties, such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area.
Any such armed attack and all measures taken as a result thereof shall immediately be reported to the Security Council. Such measures shall be terminated when the Security Council has taken the measures necessary to restore and maintain international peace and security."
Given the possibility of further similar events to that of 13th November, it might be considered that there was an attack against France albeit not by forces of another State but by non-State actors. If such a reading is accurate then this Charter would enable NATO to take "such action as it deems necessary" to assist France. Article 5 was invoked after the 11th September 2001 attacks in New York (and in other parts of the north-eastern USA). This question is discussed at Will NATO respond to the attacks in Paris but there appear to be good reasons not to invoke Article 5 as discussed in The Fiscal Times 17th November.
France did however turn to Article 42.7 of the EU Treaty - see The Guardian 17th November.