LAUSANNE, Switzerland — The White House said that a letter from Iran President Hassan Rouhani for US President Obama had been passed to US negotiators here, as top US and Iranian diplomats and nuclear experts held another intense day of closed-door meetings March 26 as negotiators try to finalize a political agreement for a final Iran nuclear deal by next week.

"I can confirm that a letter from President Rouhani to President Obama was passed to the US negotiating team in Lausanne,” Bernadette Meehan, the spokesperson for the National Security Council, told Al-Monitor in an emailed statement.

Rouhani also sent letters to the other leaders of the P5+1 (the five permanent members of the UN Security Council plus Germany), he said on Twitter, and held phone calls March 26 with British Prime Minister David Cameron, French President Francois Hollande, Russian President Vladimir Putin and his Chinese counterpart.

Cameron and Rouhani, in their first phone call ever, “expressed their commitment to securing a deal,” a spokesperson for Cameron said in a read-out of the call. “They both agreed that the ongoing discussions in Switzerland and the possibility of securing a political framework by the end of the month presented a historic opportunity.”