U.S. Secretary of State John Kerry has called Qatar's young new emir and voiced hope for further cooperation with the increasingly active nation, an official said Wednesday.

Kerry, who is on a regional tour aimed at coordinating support for Syria's rebels, spoke by telephone Tuesday with the new emir, 33-year-old Sheikh Tamim bin Hamad al-Thani, and his father Sheikh Hamad bin Khalifa al-Thani.

U.S. President Barack Obama and Afghan leader Hamid Karzai support the idea of holding talks with the Taliban in its Qatar office, the White House said Tuesday, reviving hopes for a peace process.

The announcement came despite a brazen Taliban assault on the Afghan presidential palace in the heart of Kabul Tuesday, in which three security guards and all five assailants were killed in an hour-long gunbattle.

Rulers of the Arab states of the Gulf, where aging monarchs retain power, congratulated Qatar's new young emir Sheikh Tamim bin Hamad al-Thani, whose father abdicated in his favor on Tuesday.

At the age of 33, Sheikh Tamim becomes the youngest ever sovereign in the Gulf Arab monarchies.

Qatar emir Sheikh Hamad bin Khalifa al-Thani abdicated in favor of his 33-year-old son, Sheikh Tamim, on Tuesday, in a first for the Arab world.

"I announce handing the rule over to Sheikh Tamim bin Hamad al-Thani," the 61-year-old emir said in a televised speech, adding the decision opened the way for a "young leadership.”

U.S. envoy James Dobbins on Monday said Washington was outraged at how the Taliban opened an office in Qatar that was intended as a first step towards a peace deal in Afghanistan.

"The use of the Islamic Emirate title... (and) the symbols, signs and nomenclature were incompatible with what had been understood to be the arrangement," he told reporters in Kabul.

Syrian Foreign Minister Walid Muallem said on Monday that the clashes in the Lebanese southern city of Sidon were the result of a "secret" plan to ramp up assistance to Syria's rebels.

“What's happening in Sidon in terms of terrorism and crimes is one of the results of the secret decisions taken in Doha,” al-Muallem told a press conference in Damascus.

Qatar's emir Sheikh Hamad bin Khalifa al-Thani is to transfer power in the small but economically powerful Gulf nation to his son Sheikh Tamim, the official QNA news agency reported on Monday.

"The royal palace announces that Qatar's emir, Sheikh Hamad bin Khalifa al-Thani, will address the Qatari people at 8:00 am (0500 GMT) on Tuesday," said a statement carried by the official QNA news agency.

U.S. Secretary of State John Kerry has vowed new support for Syria's rebels but beyond tougher talk, it remains unclear how much has changed.

Kerry met with fellow opponents of Syrian President Bashar Assad's regime during talks Saturday in the Gulf Arab monarchy of Qatar, a stalwart supporter of the Sunni Muslim rebels.

French President Francois Hollande arrived in Qatar on Saturday for talks on the Syrian civil war and on economic ties with the gas-rich Gulf state.

He landed in Qatar as a "Friends of Syria" meeting there earlier in the day decided to provide urgent military aid to Syria's rebels.

The United States warned Saturday that it could call on the Taliban to close an office in Qatar unless it shows more commitment to reconciliation in Afghanistan.

U.S. special envoy James Dobbins arrived in the Gulf Arab monarchy and was taking part in talks with Qatar alongside Secretary of State John Kerry.