WASHINGTON - The United States urged South Sudan's leaders on Monday to implement a Jan. 23 ceasefire between the government and rebels as an advance team of regional monitors arrived in the country.

A State Department official also pressed for the quick release by the government of the last four of a group of 11 detainees held on suspicion of trying to stage a coup, and to offer them and their families protection.

Seven of the political figures were released on January 29, partially meeting a rebel demand at peace talks.

The team of monitors arrived in South Sudan on Sunday to observe a shaky ceasefire agreed by the government of President Salva Kiir and rebels led by former vice president Riek Machar, whom he sacked in July for trying to seize power.

"We strongly support their efforts and urge the government of South Sudan and rebel leader Machar to facilitate their important work," the official said of the monitors.

"The expeditious release and transfer of all of the detainees would reduce tension and build confidence in an inclusive reconciliation process," the official added.

Thousands of people have been killed and more than 800,000 have fled their homes since fighting erupted in mid-December, triggered by a power struggle between Kiir and Machar.

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