During the course of the arbitral proceedings, a party may amend or supplement its claim or defence, including a counterclaim or a claim for the purpose of a set-off, unless the arbitral tribunal considers it inappropriate to allow such amendment or supplement having regard to the d elay in making it or prejudice to other parties or any o ther circumstances. However, a claim or defence, including a counterclaim or a claim for the p urpose of a set-off, may not be amended or supplemented in such a manner that the amended or supplemented claim or defence falls outside the jurisdiction of the arbitral tribunal.