In recent weeks, a lot has been written about the politics surrounding the military intervention in Yemen by a coalition of states led by Saudi Arabia. On one hand, Pakistan has been under pressure to join this Operation Decisive Storm and, on the other hand, the Pakistani government is under increasing pressure from Iran and certain political quarters to avoid getting involved in another country’s internal conflict. In this backdrop, it is important to analyse the legal basis on which states may or may not undertake military intervention in such situations. There are three key issues that need to be addressed in this regard: impact of the request made by and the consent given by President Hadi to the operation against the Houthis, Saudi Arabia’s framing of the dispute as a threat to its security and the question and impact of Iran’s alleged support to the Houthis.It is not uncommon on the part of cornered heads of state to seek help from members of the international community against threats to peace within their national boundaries. A recent example is that of Iraq requesting the US to help fight Islamic State (IS). Intervention by invitation can be considered legitimate under international law and may not give rise to any controversy as long as the position of the incumbent (head of state requesting support) remains lawful and without doubt. In this case, however, President Hadi perhaps does not enjoy a clear and unequivocal position as the legitimate head of state of Yemen. He initially assumed power in the 2012 elections for a term of two years, which ended in February 2014 but the term was extended for another year without fresh polls. At the beginning of this year, Mr Hadi resigned, allegedly under the pressure of the Houthis, only to revoke his resignation later once he had managed to escape Sanaa. To assess the legality of international military intervention, based on his invitation, it is imperative to determine whether his request for assistance holds official force or is without any legal effect. If Mr Hadi, who claims to be the president, acted under duress in January, tendered his resignation and later fled the country, it is only reasonable to consider whether the Yemeni forces under his command had lost effective control over territory and whether the president’s word may not be effective anymore. According to Mr Stuart Casey-Maslen, senior researcher in international law at the University of Pretoria, “Whoever controls the state represented by territory and the armed forces — in this case that would be [the Houthis].” This narrative, nonetheless, does not represent a final determination of Mr Hadi’s status as the legitimate head of state as other countries continue to consider Mr Hadi the legitimate president and his call for help is therefore being considered legitimate. Therefore, the international military response under Operation Decisive Storm against the Houthis may not be termed a violation of Article 2 (4) of the UN Charter, which prohibits member states from interfering in the domestic affairs of another state since the intervening states are relying on a call for assistance from someone they consider to be the legitimate ruler of Yemen.The second aspect of this issue is Saudi Arabia’s framing the increasing influence of the Houthis as a threat to its and the region’s security. Article 51 of the UN Charter allows states to act in self-defence only when they have been attacked. It is not entirely clear whether the news of some attacks on Saudi Arabia’s border posts is well founded, whether the Houthis from Yemen are responsible for such attacks and if such attacks pose any real threat to Saudi Arabia’s territorial security. Accordingly, it is not clear whether reliance on the principle of anticipatory self-defence will hold ground in the present circumstances. In the Caroline affair (also known as the Caroline case), through which the doctrine of preemptory self-defence stood articulated, it was established that the need for exercising the right to self-defence must be “instant”, “over-whelming”, “leaving no choice of means”, “no moment for deliberation” and the force used in response must be proportionate. As per the reports so far, the Houthis do not seem to pose imminent threat of an over-whelming nature, which could justify an attack under Article 51 of the UN Charter. It is worth noting that despite the guidelines provided for in the Caroline case, international acceptance of the concept of pre-emptive strikes remains low. Furthermore, the killing of two Saudi Arabian soldiers at border posts does not constitute an attack by Yemen, as a state, but rather can be viewed only as an attack by rebel forces. These sporadic border attacks are perhaps only good enough to engage the responsibility of the state of Yemen and probably cannot form the basis of exercising the right of pre-emptive self-defence under international law. It is important to note that Article 51 of the UN Charter was also invoked by President Hadi in his letter to the UN Security Council although it is not clear how he can request intervention pursuant to Article 51 as that would perhaps imply that Yemen was under attack from external forces. It appears that he is contending that Iran exercises effective control over the Houthis and has violated Article 2 (4) of the UN Charter. In the Nicaragua Case, the International Court of Justice laid down the test of “effective control” to determine whether interference engages the responsibility of a state. The effectiveness test would require the activities of a rebel group not only to be sponsored but directed by a state and that rebels acted upon the instructions so received. It is quite improbable that such a level of effective control by Iran over the Houthis can be proven by Yemen/President Hadi.Accordingly, in the prevailing circumstances, it seems that the only justification for attacking the Houthis, which could provide some legitimacy to the actions of the coalition states under international law, would be the request and consent of President Hadi, in relation to military action against the Houthis, as addressed in communications to the UN Security Council and various neighbouring states.Perhaps a better option for Pakistan and other states, particularly in the absence of a clear UN Security Council Resolution under Chapter Seven of the UN Charter specifically authorising military action in this case, would be to seek a solution to the conflict through mediation. Article 33 of the UN Charter, though applicable in respect of interstate disputes, advises the adoption of amicable means to settle disputes. This would further not only Pakistan’s position as a responsible member of the international community but reinforce international confidence in the mediatory provisions of the UN Charter as well. Nevertheless, if Pakistan decides to send troops as part of Operation Decisive Storm to fight the Houthis in Yemen, not only would the Pakistani government need to be convinced of and present the legal basis of taking part in such military intervention, it will also need to ensure that its forces do not take any action in breach of the applicable provisions of international humanitarian law. The writers are lawyers