He made the remarks in a press conference with representatives of domestic and foreign media here on Monday morning.
Answering a question regarding developments in Syria, the President said that the situation of region is very volatile.
Addressing the countries that support terrorists in Syria, President Rouhani said that unfortunately some regional and western states advocate the terrorists.
“During my fist participation in the UN General Assembly meeting in 2013, I told the European officials that how much dangerous supporting the terrorists is,' he added.
Rouhani said, “I told the European officials that if you continue your support for terrorists, you will witness instability in your capitals.”
He referred to terrorists’ brutal actions in Syria and said, “We believed from the beginning that terrorism in this region should be ended and the Syrian government should usher in reforms.”
“We advise referring to polling stations for resolution of regional problems,” he added.
President Rouhani pointed to the upcoming elections to be held in Iran on May 19, and said that similar to Iran, if all the regional states resort to polling stations for resolution of their problems, their troubles will decrease and finally disappear.
The President expressed the hope for realization of reform in Syria, and noted that reform in that country is quite necessary.
He, meantime, pointed to the recent US cruise missile attacks on Syria's Shayrat airbase, and said that the Americans did the attack under the pretext of an ambiguous chemical explosion.
'I told the Syrian President Bashar al-Assad and Russian President Vladimir Putin in my yesterday phone conversation that establishment of a fact-finding international committee would help recognizing the source of chemical materials used in Khan Sheikhoun.”
Rouhani criticized US for its speedy and illogical response, and noted that what will be the US answer if the investigations prove that terrorists were behind the nerve gas attack in Khan Sheikhoun.
He referred to Moscow's reaction to Washington attack, and said, 'Such actions by the US will be unanswered if they are repeated.'
“If the cruise missiles which struck the Russian forces were deployed in Khan Sheikhoun, it could ignite a big conflict.”
'I think what the Americans did is not consistent with international rules, logic and the interests of the regional countries,' he added.
President Rouhani said that therefore, the countries which encourage the US to support the terrorists are making a big mistake.
President Rouhani noted that the terrorists suffered two big defeats in Aleppo and Hama provinces of Syria, and said, 'The recent US move was possibly an action to compensate terrorists’ defeats.'
He condemned the use of chemical weapons by any side in wars, saying, 'We are a victim of chemical weapons.”
“Khan Sheikhon reminds us of the suffering of the Iranian and Iraqi people who were killed or injured in Iran’s Sardasht region and Iraq’s Kurdish region of Halabcheh after former Iraqi dictator Saddam Hussein launched a chemical attack.”
Answering another question about establishment of European Union office in Tehran, President Rouhani said that the Foreign Ministry pursues the issue and it will be done according to rules and regulations.