President Rouhani made the remarks in a telephone conversation with his Turkish counterpart Recep Tayyip Erdogan on Saturday.
"I we do not become unison against the US, big threat will jeopardize the whole region," the Iranian president said.
He stressed that the US assassination of Lieutenant Soleimani was a big mistake, adding that "if we remain silent against the US, it will become bolder and more aggressive".
President Rouhani, meantime, appreciated Turkish president for his sympathizing with the Iranian government and nation on the sad occasion of the loss of the top Iranian general. "Iran and Turkey have always cooperated on complicated issues."
"We should respond to unwise measures and remaining silent vis-à-vis the aggressor and oppressor will make them bolder," the Iranian president added.
President Rouhani said that according the Holy Quran teachings "we do not oppress and we will not be oppressed", adding, "Martyr Soleimani had a unique role in combating terrorists in the region and you are well-aware that how he fulfilled the great regional and Islamic duty."
The Iranian president said that the Iranian people are very angry with what the Americans have done, and said that what the US did was very wrong and unwise, the US has violated Iraq's national sovereignty and carried out terrorist acts in Iraq which contradicted that country's independence.
"The US also carried out an organized terrorist act against another government and martyred our great and popular military commander and if we will not be unison, we will face a great threat," President Rouhani added.
The Iranian president said that "we expect that all our friends and neighbors should explicitly condemn this crime".
Referring to the ongoing development in Syria, President Rouhani said that the efforts will continue within the framework and level of the Iranian, Turkish and Russian leader to resolve Syria problem.
The Iranian president also pointed to Iran's interest to develop bilateral ties, and said, "I hope to meet each other in Tehran soon."
The Turkish president, for his part, extended his condolences on martyrdom of Lieutenant Soleimani to Supreme Leader of the Islamic Revolution Ayatollah Seyyed Ali Khamenei, the Iranian nation and government, and said, "I was deeply saddened and I am aware of the anger and hatred of Iran's leadership, you (President Rouhani) and the Iranian nation.
President Erdogan said that he has seen the glorious funeral procession of Lieutenant General Soleimani from the Iraqi television, adding that all these scenes clearly show the Iraqi people's interest in Lieutenant General Soleimani "and I pray to God for him to rest in peace".
The Turkish president pointed to the need for restoring stability and security in the region, and said, "Foreign interferences and fighting in the region prevent the region from attaining calmness and stability and we should not allow such measures to endanger regional peace and stability."
President Erdogan pointed to talks between Iranian and Turkish foreign ministers, and said, "In my upcoming visit to Tehran in the near future, we will discuss and exchange views on bilateral ties and regional issues."
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