* Chinese peacekeeper killed
* U.S. demands immediate end to fighting
* Rival leaders had called for calm on Friday
* Fighting revives fear of return to full-blown conflict (Updates with comment from China's defence ministry)
By Denis Dumo and Michelle Nichols
JUBA/UNITED NATIONS, July 10 (Reuters) - Renewed fighting erupted in South Sudan's capital on Sunday and forces loyal to Vice President Riek Machar said his residence was attacked by the president's troops, raising fears of a slide back into full-blown conflict in the five-year-old nation.
There was no immediate response from the government of President Salva Kiir to the statement by Machar's spokesman. Kiir's information minister, Michael Makuei, said earlier the situation was under control and urged people to stay at home.
The two leaders, who fought each other in a two-year civil war that started in late 2013, had made a joint call for calm after clashes between rival factions broke out late on Thursday. At least 272 people have been killed in the fighting, a Health Ministry source told Reuters early on Sunday.
A Chinese U.N. peacekeeper was killed and several Chinese and Rwandan peacekeepers were injured, Japan's U.N. ambassador Koro Bessho said on Sunday after the U.N. Security Council was briefed on the situation. Japan is council president for July.
The U.N. mission said U.N. compounds in Juba had been hit by small arms and heavy weapons fire.
"The Security Council expressed their readiness to consider enhancing (the U.N. mission) UNMISS to better ensure that UNMISS and the international community can prevent and respond to violence in South Sudan," Bessho told reporters.
He said the 15-member council encouraged countries in the region to prepare to send additional troops in the event the Security Council decides to boost the strength of the nearly 13,500-strong U.N. force. The council also stressed the need for peacekeepers to use all means necessary to protect civilians.
The U.S. State Department on Sunday demanded an immediate end to the fighting in South Sudan and ordered the departure of non-emergency personnel from the U.S. Embassy in Juba.
"We're extremely worried about what appears to be the lack of command and control over the troops," U.S. Ambassador to the United Nations Samantha Power said on her way into the Security Council briefing, which the United States requested.
A confidential note to the council on Sunday from the U.N. Department of Peacekeeping, seen by Reuters, said: "UNMISS has adopted a proactive posture, conducting patrols within and outside" its compounds and has reinforced the perimeter security to enhance protection for displaced civilians and U.N. staff.
The note said the fighting "involved the use of attack helicopters and tanks" and that the U.N. compounds were in the cross-fire.
One U.N. Chinese peacekeeper was killed and six were others injured when the armoured vehicle in which they were travelling was shelled.
China's defence ministry issued a statement on Monday condemning the attack, and said it would strengthen safety measures.
U.N. Secretary-General Ban Ki-moon said Kiir and Machar needed to take "decisive action" to regain control of the security situation in Juba and urged them to order their forces to disengage and withdraw to their bases.
"I am deeply frustrated that despite commitments by South Sudan's leaders, fighting has resumed," Ban said in a statement. "This senseless violence is unacceptable and has the potential of reversing the progress made so far in the peace process."
Residents of Juba's Gudele and Jebel districts reported heavy gunfire near the barracks where Machar and his troops have their headquarters.
The Health Ministry source said 33 civilians were among those killed in the latest clashes, which have fuelled fears about renewed conflict and raised concerns about the extent the two men can control their troops in the world's newest nation.
"We have called for an arms embargo, we think that this (violence) absolutely underlines the need for that and we are prepared to look at any measures that are necessary in order to stop this violence," Britain's deputy U.N. ambassador, Peter Wilson, said on his way into the council meeting.
Earlier this year, Security Council veto power Russia said it was opposed to an arms embargo because Moscow did not believe it would be helpful to the implementation of a peace deal agreed to by Kiir and Machar last August.
When asked on Sunday about the possibility of a arms embargo, Russia's deputy U.N. ambassador, Vladimir Safronkov, said the council needed to do "something serious about stabilising the political situation."
The confidential U.N. peacekeeping note said some 3,000 civilians, including senior opposition officials, had sought shelter at one U.N. site, while 800 other civilians had entered a second U.N. compound.
"Dr. Machar's residence was attacked twice today including using tanks and helicopter gunships. Helicopters from Kiir's side attacked the residence twice," Machar's spokesman, James Gatdet Dak, told Reuters by phone from abroad.
He added that the situation in Juba had subsequently calmed, echoing comments from residents who said gunfire had eased later on Sunday after several hours of shooting.
The fighting first erupted on Thursday, when troops loyal to Kiir stopped and demanded they be allowed to search vehicles of Machar's loyalists. That stand-off led to clashes.
Gunfire broke out again on Friday between the vice president's bodyguards and the presidential guard, while the two men were holding talks at the presidential State House to defuse tensions. Both men said at the time they did not know what had prompted the exchange of fire.
Kenya's presidency urged Kiir and Machar to move heavy weaponry and troops out of civilian areas in Juba. It said Kenya was ready to support law enforcement. Kenya Airways has suspended flights to Juba.
Machar and Kiir spent months wrangling over details after signing the peace deal last year. Machar finally returned to Juba to resume his former position as vice president in April.
Fighting since 2013 has left large areas of the country of 11 million people struggling to find enough food. It has also disrupted oil production, by far the government's biggest source of revenue. (Additional reporting by George Obulutsa in Nairobi and Brenda Goh in Shanghai; Writing by Elias Biryabarema and Edmund Blair; Editing by Paul Simao and Peter Cooney)
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