0513 GMT January 20, 2019
"I believe that old, friendly and constructive ties between the Islamic Republic of Iran and the German Federal Republic have provided the two countries with an appropriate opportunity to expand mutual relations more than ever," Rouhani said in a message to Merkel on Monday, Press TV reported.
It is expected that the two countries would further improve relations based on mutual respect and common interests, he added.
The German chancellor, bruised by half a year of post-election coalition haggling, was elected by parliament to her fourth and likely final term at the helm of Europe's biggest economy on Wednesday.
Lawmakers in Berlin's glass-domed Reichstag voted 364-315 with nine abstentions for Merkel, who was then to be formally appointed by President Frank-Walter Steinmeier before taking the oath of office.
Also in his message, Rouhani hailed Germany's "constructive and influential" role during the negotiations between Iran and major world powers on Tehran's nuclear program which led to the conclusion of the landmark nuclear agreement, officially known as the Joint Comprehensive Plan of Action (JCPOA), in 2015.
The Iranian president called for the "continuation of this approach to fully and successfully implement the JCPOA and counter illegitimate excessive [demands] in this regard."
Iran and the five permanent members of the United Nations Security Council – the United States, France, Britain, Russia and China – plus Germany signed the nuclear agreement on July 14, 2015 and started implementing it on January 16, 2016.
Under the JCPOA, Iran undertook to put limits on its nuclear program in exchange for the removal of nuclear-related sanctions imposed against Tehran.