UN Secretary-General Ban Ki-moon underlined the necessity of probe into the use of chemical weapons by terrorists against the people in Syria, calling it a \"dreadful and unacceptable crime\".Ban Ki-moon made the remarks in a letter to Iranian Foreign Minister Ali Akbar Salehi who had sent him a letter to ask for a UN probe into the case. Salehi\'s letter was released as a UN document later.\"We have announced many times that using chemical weapons is a dreadful and unacceptable crime,\" Ban said in his letter on Monday.He said that the main goal of investigation into the case of the chemical weapons in Syria is understanding the realities and presenting a report to the member states, and expressed the hope that probing the case would send a strong message in support of the international ban on the use of chemical weapons and \"reinvigorate our joint efforts for a permanent ban on the use of these weapons\".In a March letter to Ban Ki-moon, Salehi condemned the terrorist act of the Syrian rebels in using chemical weapons against the nation, and called on the international body to adopt preventive measures to stop repetition of such accidents.The letter, a copy of which was also sent to president of the UN Security Council, pointed to the massacre of a number of defenseless Syrian civilians in the city of Aleppo by terrorist groups, and stressed that the act was a serious threat to the international peace and security.Salehi said it also clearly negated the international legal norms, including the convention on banning the use of chemical weapons.Salehi reiterated that Iran as the biggest victim of chemical weapons has always condemned the terrorist approach of the Syrian rebels and expected all governments and international organizations, including the UN to strongly condemn such behavior and spare no efforts to prevent its recurrence.He also urged them to carry out an impartial investigation to find out supporters and sponsors of the inhuman act.Noting that the crime was committed on the threshold of the third conference to revise regulations relating to the chemical weapons, Salehi emphasized the need for the thorough, effective and indiscriminate implementation of the convention by signatory countries, specially the absolute elimination of destructive weapons by their owners.The letter concluded by stressing that use of chemical weapons by governments and dissident groups under any conditions was unacceptable.Earlier in March, terrorists fired a rocket containing chemical substances in the Khan al-Assal area of rural Aleppo and reports indicated that around 25 people were killed, most of them civilians.After that Syria asked for an independent investigation into the use of chemical weapons by militants in Aleppo.Later, Ban Ki-moon announced the decision for conducting an independent investigation into the terrorist chemical attack.\"I have decided to conduct a United Nations investigation into the possible use of chemical weapons in Syria,\" Ban told reporters in his office, adding that \"I intend for this investigation to start as soon as practically possible.\"The chemical attack came after a video footage posted on the internet late in January showed that the armed militants in Syria possessed canisters containing chemical substances.The foreign-sponsored militants had earlier released footage in which rabbits were killed by inhaling poisonous gas.