Iran’s President Hassan Rouhani addresses a plenary meeting of the United Nations Sustainable Development Summit 2015 at the United Nations headquarters in Manhattan, New York.

Iran’s President Hassan Rowhani said on Sunday fighting radical militants like ISIS in Syria is the top priority and if they are to be defeated then President Bashar al-Assad’s government “can’t be weakened.”

“This does not mean that the Syrian government does not need reform … Of course it does,” Rowhani told an audience of U.S. think-tanks and journalists on the sidelines of the U.N. General Assembly meeting in New York, but he added that the removal of his ally Assad would turn Syria into an extremist safe haven.

Discussions of political reform in Syria should come after the threat of extremism in Syria has been removed.

Separately, Iran’s state news agency IRNA said Rowhani will cut short his visit to New York and return to Tehran for the funeral of Iranians killed in the hajj tragedy in Saudi Arabia, Iran’s state news agency IRNA reported on Sunday.

“Some of his meetings and scheduled programs will be canceled and he is returning (to Tehran) on Monday afternoon,” IRNA quoted a senior official from Rowhani’s office as saying.

Earlier, Rowhani said in an interview that he was ready to discuss a “plan of action” for Syria’s post-war future after ISIS is defeated.

Iran, which along with Russia is allied with Assad in the war, has until now been kept out of U.N. diplomatic efforts to piece together a political solution for Syria.

“That is not a problem for us from right now, to start holding discussions and dialogues so as to determine and reach the conclusion of the next plan of action after the terrorists are driven out that territory,” Rowhani said in an interview to NPR radio.

“But we must all act in unison and have a formula that is required to drive out the terrorists, immediately.”

Rowhani is expected to address the crisis in Syria in his speech to the U.N. General Assembly on Monday, after President Barack Obama and Russian leader Vladimir Putin take the podium.

The Iranian leader said his country was ready to discuss “the upcoming options” and added that the Syrian government should be included to “reach a plan of action.”

Tehran has been providing financial and military support to the Damascus regime as well as military advisers on the ground in Syria, where more than 240,000 people have died and four million people have been driven from their homes.

Western powers are seeking to enlist Iran in a new strategy to address the crisis after Russia beefed up its military presence in Syria in a bid to gain the upper hand on the future political transition.

The West has softened its demands for Assad to leave power, signaling that the president could stay on in an interim role as part of a two-stage transition.

Rowhani added that the Syrian people must “have the last word and most important word” on the future of the county, in reference to elections that could cap an interim transition.

Seperately, President Francois Hollande told his Iranian counterpart in a meeting on Sunday, that Iran can be a facilitator in a political solution in Syria but President Bashar al-Assad cannot be part of it, according to a French official.

“Iran is a player (in the region), but also a facilitator,” the official, speaking on condition of anonymity, said. “(Hollande) said that the question of Assad could not be offered as an answer.”

Hollande also offered his condolences to Rowhani following the hajj tragedy, but cautioned that the incident should not add to tensions between Iran and Saudi Arabia, the official added.