US Deputy Secretary of State William Burns, who holds the highest rank in the foreign service, will retire in October, the State Department said Friday.

Burns informed Secretary of State John Kerry of his decision in a letter.

Burns, who having served ten secretaries of State in his 32- year career on the foreign service, holds the rank of career ambassador, the highest in the foreign service. He took his current post in July 2011. Before that, he also served the posts including as assistant secretary of state for Near Eastern affairs, US ambassador to Russia, and as under secretary of state for political affairs.

In 2012, he was asked by President Barack Obama to lead a secret back channel of negotiations with Iran over its controversial nuclear program, an effort that produced a first- step agreement in November and ongoing negotiations over a comprehensive deal between Iran and the six world powers.

Obama, who had made Burns delay his retirement, spoke highly of the diplomat in a statement.

Kerry also heaped praise on Burns, saying "It's not just where he's served, it's who he is and what he's done. This guy is the real deal."

"With characteristic humility, he has enormous impact and influence in untold ways and myriad issues," said Kerry.