In statements, three Iranian leaders - President Hassan Rohani, Foreign Minister Zarif, and Deputy Foreign Minister and senior negotiator Abbas Araghchi - emphasized that Iran has no intention of abiding by UNSRC 2231, which includes the JCPOA and another element; rather, that they will abide only by the original JCPOA.
The Iran nuclear deal consists of the following:
A. A set of understandings between Iran and the P5+1 powers (as well as the remaining disagreements) all in a single package called the JCPOA. It is not a contract between Iran and the P5+1 countries as a group or any single one of them, and hence no document was signed.
B. This set of mutual understandings (as well as disagreements) packaged in the JCPOA was transferred, following the conclusion of negotiations in Vienna on July 14, 2015, to the UN Security Council, for endorsement as a UN Security Council resolution. The resolution, UNSCR 2231, was passed on July 25, 2015 and it includes, in addition to the JCPOA, another element (Annex B) with further stipulations regarding Iran. For example, it addresses the sanctions on Iran's missile development project.
To understand why UNSCR 2231 is structured in this way, we can look at statements by top Iranian negotiators about the process that led up to it:
In a July 20, 2015 interview on Iranian Channel 2, Iranian Deputy Foreign Minister and senior negotiator Abbas Araghchi said that there had been tough bargaining between the Iranian and American delegations over the issue of the arms embargo on Iran and the sanctions related to Iran's missile development project. "The Americans sought their inclusion in the JCPOA, claiming that otherwise they could not face criticism from Arab countries in the region. When they said that they could not lift the sanctions altogether, we told them explicitly that in that case there is no agreement. We told them that the national security issues are non-negotiable and that we will not accept an agreement which continues the embargo on weapons and the sanctions on missile development. In the end, the Americans said, We will put the issue of the embargo and the missiles in the UN Security Council Resolution separate from the agreement."
In the same interview, Araghchi was asked whether Iran could refrain from carrying out UNSCR 2231; he replied: "Yes we can; just as we refrained from complying with UN Security Council resolutions, we can do so with regards to 2231."
Araghchi also referred to the Iranian Foreign Ministry statement issued following the passage of UNSCR 2231: "The Iranian Foreign Ministry statement explicitly noted that Iran does not attach legitimacy to any restriction and any threat. If UNSCR 2231 will be violated by Iran, it will be a violation of the Security Council resolution and not of the JCPOA, similar to what happened 10 years ago when we violated Security Council resolutions and nothing happened. The text of the JCPOA notes the fact that the content of the JCPOA and of the UN Security Council resolution are two separate things."
Foreign Minister Zarif, in an August 9, 2015 media interview, reiterated the Iranian position regarding the difference between the JCPOA and UNSCR 2231, with a focus on the consequences of possible violation of the two by Iran. He said: "There is a difference between the JCPOA and UNSCR 2231. Violating the JCPOA has consequences, while violating UNSCR 2231 has no consequences."
Indeed, the restrictions regarding missiles are mentioned only in UNSCR 2231, and not in the JCPOA.
On August 29, 2015, Iranian President Hassan Rohani said: "There is nothing about the topic of missiles, defense, and weapons in the JCPOA. Whatever we have about it is in Resolution [UNSCR] 2231... Moreover, we have formally announced that we are not committed to all the sections that appear in the resolution , and we specified in the JCPOA that violation of the resolution  does not mean violation of the JCPOA...
The meaning of all this is that in everything related to the issue of missile development, Iran will disregard UNSCR 2231. Already during the negotiations, it insisted on no imposition of sanctions on Iran regarding its missile development (and no sanctions at all). When the Americans moved the sanctions on the missile program to UNSCR 2231, Iran did not object, as, according to their statements above, they can violate Security Council resolutions, as they have done in the past, and this will not be regarded as a violation of the JCPOA.
 ISNA.ir/fa/news/94042915462/%D9%85%D9%85%D9%86%D9%88%D8%B9%DB%8C%D8%AA-%D9%87%D8%A7%DB%8C-%D8%AA%D8%B3%D9%84%DB%8C%D8%AD%D8%A7%D8%AA%DB%8C-%D9%88-%D9%85%D9%88%D8%B4%DA%A9%DB%8C-%D8%A8%D9%87- .
 President.ir/fa/89047, August 30, 2015.