Following the links provided by indigochild I searched a bit more and found the following in the CWC. Mostly I copied and pasted the parts I found most relevant and I added some comments in brackets.
Verification Annex Part XI. Investigations in Cases of Alleged Use of Chemical Weapons
Investigations of alleged use of chemical weapons, or of alleged use of riot control agents as a method of warfare, initiated pursuant to Articles IX or X, shall be conducted in accordance with this Annex and detailed procedures to be established by the Director-General.
The following additional provisions address specific procedures required in cases of alleged use of chemical weapons.
B. Pre-Inspection Activities
Request for an investigation
The request for an investigation of an alleged use of chemical weapons to be submitted to the Director-General, to the extent possible, should include the following information:
(a) The State Party on whose territory use of chemical weapons is alleged to have taken place;
(b) The point of entry or other suggested safe routes of access;
(c) Location and characteristics of the areas where chemical weapons are alleged to have been used;
(d) When chemical weapons are alleged to have been used;
(e) Types of chemical weapons believed to have been used;
(f) Extent of alleged use;
(g) Characteristics of the possible toxic chemicals;
(h) Effects on humans, animals and vegetation;
(i) Request for specific assistance, if applicable.
The State Party which has requested an investigation may submit at any time any additional information it deems necessary.
[...goes on to paragraph 27.]
The relevant parts of Article IX seems to be:
- Without prejudice to the right of any State Party to request a challenge inspection, States Parties should, whenever possible, first make every effort to clarify and resolve, through exchange of information and consultations among themselves, any matter which may cause doubt about compliance with this Convention, or which gives rise to concerns about a related matter which may be considered ambiguous. A State Party which receives a request from another State Party for clarification of any matter which the requesting State Party believes causes such a doubt or concern shall provide the requesting State Party as soon as possible, but in any case not later than 10 days after the request, with information sufficient to answer the doubt or concern raised along with an explanation of how the information provided resolves the matter.
[Note that it says "should , whenever possible" whatever that is supposed to mean. Also note that the 10 days deadline was mentioned by Lavrov according to RT. This suggests he may have been referring to this paragraph or alternatively to part (b) of paragraph 4 in the following. Continuing:]
Procedure for requesting clarification
A State Party shall have the right to request the Executive Council to assist in clarifying any situation which may be considered ambiguous or which gives rise to a concern about the possible non-compliance of another State Party with this Convention. The Executive Council shall provide appropriate information in its possession relevant to such a concern.
A State Party shall have the right to request the Executive Council to obtain clarification from another State Party on any situation which may be considered ambiguous or which gives rise to a concern about its possible non-compliance with this Convention. In such a case, the following shall apply:
(a) The Executive Council shall forward the request for clarification to the State Party concerned through the Director-General not later than 24 hours after its receipt;
(b) The requested State Party shall provide the clarification to the Executive Council as soon as possible, but in any case not later than 10 days after the receipt of the request;
[goes on until (f) and paragraph 25. This last one leads to redress. For more see Article IX]
In Article X the relevant parts seem to be:
Each State Party has the right to request and, subject to the procedures set forth in paragraphs 9, 10 and 11, to receive assistance and protection against the use or threat of use of chemical weapons if it considers that:
(a) Chemical weapons have been used against it;
(b) Riot control agents have been used against it as a method of warfare; or
(c) It is threatened by actions or activities of any State that are prohibited for States Parties by Article I.
The request, substantiated by relevant information, shall be submitted to the Director-General, who shall transmit it immediately to the Executive Council and to all States Parties.
[... continues with some time limits etc. Ends with paragraph 11. For more see Article X]