The Foreign Affairs Department is advising Canadians to avoid travel to South Sudan.

In an advisory issued late Monday night, Foreign Affairs also urged any Canadians still in the war-torn nation to get out as soon as possible.

Earlier Monday, civilian helicopters evacuated U.S. citizens from Bor, which has seen bouts of heavy machine-gun fire, but 3,000 citizens from countries including Canada, Britain and Kenya remain trapped there, a top UN official said Monday.

Toby Lanzer, the UN's humanitarian co-ordinator, said Australians, Ugandans and Ethiopians are also among 15,000 total people seeking protection at a UN base in Bor, a city that could see increasing violence in coming days.

The death toll from a week of violence in South Sudan has likely surpassed 1,000 people, though there are no firm numbers available, he said. The number of internal refugees has likely surpassed 100,000, said Lanzer, who is seeking urgent financial assistance from the international community.

"I can't afford any delays from donor capitals right now," he told The Associated Press in a phone call. "Never has there been a greater time of need in South Sudan."

Secretary General Ban Ki-moon is urging the UN Security Council to add 5,500 troops and police to the 7,000-strong UN peacekeeping mission in conflict-wracked South Sudan.

Ban proposed in a letter to the council obtained Monday by The Associated Press that the troops be transferred from UN missions in Congo, Darfur, Abyei, Ivory Coast and Liberia along with three attack helicopters, three utility helicopters and a C-130 military transport plane.

France's UN Ambassador Gerard Araud, the current council president, said he expects the council to vote Tuesday on a resolution authorizing the transfers.

Bor is the city where rebel forces fired on three U.S. military aircraft on Saturday, forcing the Ospreys — advanced helicopter-airplane hybrids — to abort their evacuation mission. On Sunday the U.S. evacuated Americans by civilian U.S. and UN helicopters.

The U.S. over the last week has evacuated 380 Americans and 300 others from South Sudan, which has seen vicious, ethnically targeted violence pulse through the nation. Military commanders loyal to the country's ousted vice-president have defected and say they are now in control of regions that hold lucrative oil fields.

Lanzer, who spent the weekend in Bor, said the city is experiencing tense, sporadic clashes and "fairly consistent gunfire and heavy machine-gun fire."

Canada's Department of Foreign Affairs says about 100 Canadian citizens have registered with the department in South Sudan, according to the CBC's James Fitz-Morris. There could be many more who haven't registered since it's voluntary.

U.S. troops wounded during evacuation

The violence began late on Dec. 15. South Sudan President Salva Kiir, an ethnic Dinka, said last week that an attempted military coup had triggered the violence, and the blame was placed on former Vice-President Riek Machar, an ethnic Nuer. Other officials have since said a fight between Dinka and Nuer members of the presidential guard triggered the fighting, which spiralled across the country.

South Sudan's central government lost control of the capital of a key oil-producing state on Sunday, the military said, as renegade forces loyal to a former deputy president seized more territory in fighting that has raised fears of full-blown civil war in the world's newest country. (UNMISS/Associated Press) Analysts have suggested that a tribal militia known as the White Army — from the Lou Nuer ethnic group — is moving toward Bor, which is populated by Dinkas. Lanzer said he couldn't say anything with precision about those reports.

"Everybody knows that Bor is a strategic location," he said. "It would be difficult for me to imagine a scenario in which Bor is completely calm and safe over the coming days," he said, adding that he thinks violence could become "very heavy," which is why the UN is fortifying its position there.

The U.S. over the weekend deployed about 46 troops to help evacuate American citizens. That was in addition to 45 troops sent to the capital, Juba, last week to protect the U.S. Embassy. Four U.S. troops were wounded in the evacuation attempt Saturday.

U.S. President Barack Obama over the weekend sent a letter to congressional leaders letting them know he may take further military action in South Sudan to protect U.S. citizens, personnel and property.

Fighting continued over the weekend, as the central government acknowledged it has lost control of Bentiu, the capital Unity, a key oil-producing state.

East African leaders are leading diplomatic efforts to avoid a full-blown civil war. South Sudan experienced decades of war with Sudan, which it peacefully broke away from in 2011.