On what basis can the US push for sanctions of Iran's missile activities at the UN?
On the basis that there is a 2015 UN security council resolution that bans Iran from certain types of missile testing and that Iran's recent 2019 actions contravene this resolution.
See Appendix 1 for details and supporting references.
Why does Iran get a ban on weapons testing but the USA and Russia gets to withdraw from the INF and immediately test weapons, and no UNSC resolution is forthcoming?
The cynical would say because Iran is not currently a member of the UN Security Council (UNSC) but USA and Russia are. In fact the USA and Russia are permanent members of the UNSC. Iran is one of many UN General Assemby (UNGA) member countries that only get to be on the UNSC occasionally. There are very limited UNSC seats available and very many UNGA members. This means Iran has to rely on the sympathetic veto of one of a rotating handful of other UNSC members but the USA and Russia are always able to veto any proposed UNSC resolution aimed at them. This in turn means other UNSC members see little point in proposing resolutions aimed at banning USA or Russian nuclear-capable missiles or nuclear-capable missile tests etc.
The less cynical might argue that this situation arises because there is a general desire to prevent nuclear proliferation. This general desire is accompanied by a pragmatic recognition that preventing proliferation is both desirable and more achievable than persuading existing nuclear states to give up existing capabilities. In fact the former aim (prevent proliferation) is very plausibly a necessary prior step for the latter aim (general denuclearisation).
According to the UN
To become a member of the UN, a state must follow a certain procedure. First, the state that wants to become a member of the United Nations must declare that it will adhere to the UN Charter.
The Charter has a several requirements of member states. For example, Article 2 includes
All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations.
All Members shall give the United Nations every assistance in any action it takes in accordance with the present Charter, and shall refrain from giving assistance to any state against which the United Nations is taking preventive or enforcement action.
Chapter 7 outlines actions that can be authorised through the UN including
The Security Council may decide what measures not involving the use of armed force are to be employed to give effect to its decisions, and it may call upon the Members of the United Nations to apply such measures. These may include complete or partial interruption of economic relations and of rail, sea, air, postal, telegraphic, radio, and other means of communication, and the severance of diplomatic relations.
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.
There are media reports that
Iran has test-fired a new missile, Revolutionary Guard commander Major General Hossein Salami said Saturday, according to the semi-official Tasnim news agency.
"Our country is always the arena for testing a variety of defense and strategic systems and these are non-stop movements towards the growth of our deterrent power," Salami said. "And yesterday was one of the successful days for this nation."
a U.S. official told The New York Times on Thursday that Iran had test-fired a medium-range Shahab-3 ballistic missile on Wednesday, in violation of a U.N. Security Council resolution.
UN security council resolution 2231 [...] bans Iran from undertaking ‘any activity related to ballistic missiles designed to be capable of delivering nuclear weapons, including launches using such ballistic missile technology’.”
UNSC Resolution 2231
UN Security Council Resolution 2231 states
- Iran is called upon not to undertake any activity related to ballistic missiles designed to be capable of delivering nuclear weapons, including launches using such ballistic missile technology, until the date eight years after the JCPOA Adoption Day or until the date on which the IAEA submits a report confirming the Broader Conclusion, whichever is earlier.
It also lists sanctions.
Note that the resolution was passed unanimously. That means it is insufficient for the USA to want something. Russia, China etc also have to have wanted the same thing.