US President Barack Obama on Thursday paid tribute to late Saudi King Abdullah as a bold leader and valued friend who made an enduring contribution to Middle East peace.
"As a leader, he was always candid and had the courage of his convictions," Obama said in a written statement soon after the royal court announced the king's death.
"As our countries worked together to confront many challenges, I always valued King Abdullah's perspective and appreciated our genuine and warm friendship," said Obama.
"The closeness and strength of the partnership between our two countries is part of King Abdullah's legacy."
US Vice President Joe Biden said in a statement: "In the coming days, I will be leading a Presidential delegation representing the United States to pay our respects and offer condolences to King Abdullah’s family and nation."
During Abdullah's nearly decade-long reign -- which spanned the Arab Spring and multiple wars that roiled the Middle East -- Saudi Arabia and the United States remained staunch allies.
Obama praised Abdullah's "steadfast and passionate belief in the importance of the US-Saudi relationship."
The 41st US president George H. W. Bush hailed a "dear friend and partner" whom he described as a "wise and reliable ally."
King Abdullah bin Abdulaziz, believed to be around 90 years old, was hospitalized in December suffering from pneumonia and had been breathing with the help of a tube.
He died on Thursday at 2200 GMT and will be buried Friday following afternoon prayers, according to the Saudi government.
It was not immediately clear if Obama would attend the funeral.
The president nonetheless praised Abdullah's efforts to foster peace between Palestinians and Israelis.
"He took bold steps in advancing the Arab Peace Initiative, an endeavor that will outlive him as an enduring contribution to the search for peace in the region."
At home, Obama said the king was "dedicated to the education of his people and to greater engagement with the world."
US Secretary of State John Kerry paid tribute to Abdullah saying "the world has lost a revered leader."
"He was so proud of the Kingdom’s journey, a brave partner in fighting violent extremism who proved just as important as a proponent of peace," Kerry said in a statement.
Members of Congress also paid tribute.
Republican Senator John McCain described Abdullah as an "important voice for reform in Saudi Arabia."
"He pushed for the modernization of the education system, curbed the authority of the religious police, and extended women the right to vote and run in municipal elections."
Abdullah's half-brother Salman, 79, has been named king.