The US secretary of state acknowledged Iran's critical role in the success of a political process instituted by international parties to the Syria peace talks to end the crisis in the war-torn country.
John Kerry also said in an interview with Orient TV on Saturday that the political resolution requires Iran, Russia and the Syrian government to agree to "whatever that resolution is".
"Whether or not that can happen in the current situation–the current dynamics–remains to be seen," he said.
The five-year-old civil war has left over 250,000 people dead and millions displaced in the Arab country, where a patchwork of armed groups have been fighting the forces of President Bashar al-Assad, seeking to oust him.
Syria relies on support from Iran and Russia, while militants act as proxy for Saudi Arabia and its regional and western allies, which have been conducting an air campaign there for over a year led by the United States.
Russia began intervening in the war with its own airstrikes in late September to target the self-styled Islamic State terrorists who have captured large areas of Syria and neighboring Iraq.
Kerry underlined the need to reach a consensus among the countries concerned through dialogue and diplomacy, cautioning that "additional pressure" and force could lead to "more destruction, more death, more war" and would only be considered as a last resort.
"And people are trying right now to not talk about that, but rather, to talk about the possibilities of a political solution," he said.
The top US diplomat noted that if the Syrian government does not live up to its responsibilities and if the Iranians and the Russians do not hold Assad to the promises that they have made to the international community, "then the international community obviously is not going to sit there like fools and watch this".
"There will be an increase of activity to put greater pressure on them," he said.
Kerry dismissed speculation that with the Iran nuclear deal now in force, a rapprochement in Tehran-Washington relations is in sight, saying differences between the longtime foes remain, as the negotiations leading to the accord failed to cover beyond the Iran nuclear issue.
"Well, it's a lot of speculation. It's a lot of speculation. We made it clear that the agreement we reached with Iran was about nuclear weapons—not about the region, not about the war in Syria, not about other issues–and as you know, we have differences with Iran with respect to a number of issues. So we have to wait and see. There's no clarity. There's no understanding," he said.
The July 14 nuclear deal was clinched with P5+1 (the five permanent members of the UN Security Council plus Germany) to settle a 12-year standoff over Tehran's nuclear program by placing it under temporary curbs in return for relief from international sanctions.
