(CNN) — U.S. President Barack Obama spoke by telephone Friday with Iranian President Hassan Rouhani — the first direct conversation between leaders in Washington and Tehran since 1979 — raising the possibility a deal can be reached over Iran’s controversial nuclear program.

Describing the conversation as a starting point, Obama said he believes an agreement is possible regarding Iran’s nuclear ambitions that could lead to better relations.

“While there will surely be important obstacles to moving forward and success is by no means guaranteed, I believe we can reach a comprehensive solution,” Obama told reporters during a White House briefing.

Western leaders have expressed cautious optimism about Iran’s more moderate tone under Rouhani, whose recent comments have raised hopes that a deal could be struck over the Middle Eastern nation’s nuclear program.