In his speech before the United Nations on Wednesday, President Obama stated that “over 40 nations have offered to join this coalition” to dismantle the Islamic State of Iraq and the Levant (ISIL). That number includes countries that have committed military and nonmilitary assistance, and it includes those states that have been directly engaged in military operations inside Iraq or Syria.

On Wednesday, the Dutch government announced that it would send F-16 jets to fight ISIL alongside the United States in Iraq. And British Prime Minister David Cameron has announced that he is recalling Parliament on Friday to decide whether “Britain can take part in international air strikes against ISIL in Iraq.”

The United States has, however, experienced more difficulty in obtaining support from some of its traditional allies in conducting airstrikes inside Syria.

Ambassador Samantha Power’s letter to UN Secretary-General Ban Ki-moon stated that the US airstrikes in Syrian territory were consistent with the UN Charter because Syria had proven “unwilling or unable to prevent the use of its territory” for attacks by ISIL against Iraq.

That legal position is not shared by some other governments.

In announcing his government’s decision to send F-16s to Iraq, Dutch Deputy Prime Minister Lodewijk Asscher told reporters that the Netherlands will not take part in the military mission in Syria. He stated, “For military operations in Syria, there is currently no international agreement on an internationally legal mandate.”

Last week Australian Prime Minister stated in an interview that it was “perfectly legal under international law” to conduct military operations in Iraq due to the Iraqi government’s approval. When asked by the interviewer whether the military force inside Syria would require approval, he replied:

“President Obama has certainly indicated that US forces will strike ISIL inside Syria if needs be. That is not Australia’s intention at this time. I don’t rule it out but it is not our intention at this time because as you rightly say the legalities of operating inside Syria … are quite different from the legalities of operating inside Iraq at the request and in support of the Iraqi government.”

Last week, French President Francois Hollande announced that France will join U.S.-led airstrikes in Iraq, but he ruled out French participation in airstrikes in Syria. “We’re very concerned with the aspects of international law,” Hollande said. “We’ve been called in by the Iraqis, we’re not called on in Syria.’ [Update: The French Foreign Minister has said that France’s top military officials are meeting Thursday to decide whether to join the military coalition in Syria, and that there is no “legal obstacle” to airstrikes in Syria.]

Notably British Prime Minister Cameron made clear that the Parliament debate set for Friday will be confined to a question of airstrikes against ISIL based in Iraq, not Syria. Opposition Labour leader Ed Miliband has reportedly “indicated he would not support British military action against ISIS in Syria unless there was a United Nations Security Council resolution authorizing it.”