Already head of the main ruling party, Zardari becomes one of the most powerful civilian leaders in Pakistan's turbulent 61-year history. Last month, he marshaled a coalition that forced longtime U.S. ally Musharraf to quit as head of state.
Zardari, a novice leader untested on the international stage and stained by past corruption allegations, takes over at a critical time for the volatile, nuclear-armed Muslim nation of more than 160 million.
Pakistan's economy is crumbling, and Saturday's attack was the latest in a string of suicide bombings usually claimed by Islamic militants who have steadily gained strength since Pakistan joined the U.S. war on terrorism in 2001.
Washington is pressing Pakistan hard to eradicate Taliban and al-Qaida havens near its border with Afghanistan. An American-led ground attack said to have killed at least 15 in Pakistani territory Wednesday sparked outrage and embarrassed Zardari's party.
U.S. reactionRob McInturff, a State Department spokesman, extended congratulations to Zardari.
"Our position has been and has long been that we support the democratic process in Pakistan and we hope the government will focus on the challenges facing the country and the needs of its people," McInturff said.
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