NAIROBI, Kenya - British, Canadian and Kenyan citizens are among 3,000 foreigners trapped in a South Sudan city experiencing bouts of heavy machine gun fire, one of the most violent areas of a weeklong conflict that has likely killed more than 1,000 people, a top U.N. official said Monday.

Australians, Ugandans and Ethiopians are also among 17,000 people seeking protection at a U.N. base in Bor, a city that could see increased violence in coming days, said Toby Lanzer, the U.N.'s humanitarian coordinator.

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 is probably more than 100,000, said Lanzer, who is seeking urgent financial assistance from the U.S., Britain and other European countries.

"I know there are many thousands of people seeking protection in churches," Lanzer said. "I know that we have our own staff that have literally walked into the bush and are communicating from there. That's where they say they are safest."

U.N. Secretary-General Ban Ki-moon urged the Security Council late Monday to add 5,500 troops and police to the 7,000-strong U.N. peacekeeping mission in South Sudan, citing growing violence in many parts of the country, human rights abuses, "and killings fueled by ethnic tensions."

Ban proposed in a letter to the council obtained by The Associated Press that the troops be transferred from U.N. missions in Congo, Darfur, Abyei, Ivory Coast and Liberia, along with three attack helicopters, three utility helicopters and a C130 military transport plane.

After an emergency Security Council meeting, France's U.N. Ambassador Gerard Araud, the current council president, said the council will vote on a U.S.-drafted resolution authorizing the transfers at 3 p.m. EST (2000 GMT) on Tuesday. He said there was "a positive reaction" from all 15 council members.

The secretary-general called on member states to urgently provide transport to get the troops, police and equipment to South Sudan.

He said the U.N. mission's capacity to investigate human rights abuses is also being urgently strengthened.

Ban said the situation in South Sudan "is of mounting urgency," with tens of thousands of people displaced and about 45,000 seeking protection at U.N. bases.

He said he was spending most of Monday urging regional leaders to increase military support and "political backing for efforts to defuse the crisis."

In a message to the Sudanese people, the secretary-general said: "The United Nations will stay with you. We will do our utmost to protect you, to provide the humanitarian assistance you need, and most of all to help the country regain the path to peace."

Samantha Power, the U.S. ambassador to the U.N., told reporters "the future of South Sudan is in jeopardy."

"The leaders of South Sudan face a stark choice," she said. "They can return to the political dialogue and spirit of cooperation that helped establish South Sudan or they can destroy those hard-fought gains and tear apart their newborn nation."

The violence began late on Dec. 15. South Sudan President Salva Kiir, an ethnic Dinka, has said an attempted military coup triggered the violence, and the blame was placed on ousted former Vice President Riek Machar, an ethnic Nuer. Other officials have since said a fight between Dinka and Nuer presidential guards triggered the fighting.

South Sudan experienced decades of war with Sudan, which it peacefully broke away from in 2011.

East African leaders and the United States are pushing diplomatic efforts to avoid a full-blown civil war.

U.S. special envoy for South Sudan, Donald Booth, met Kiir on Monday.

A senior U.S. official said both Kiir and Machar said they were willing to talk to each other, and that their stated commitments indicated that there is a "good possibility of getting them together." But a lot of details, including the time, venue and circumstances of such a meeting as well as the specifics of what they would discuss, still need to be determined, the official said.

Power said Booth also met with 11 detained opposition leaders Monday and reported that they are "secure and well and very open to ending the crisis through dialogue and reconciliation."

Rebel forces fired on three U.S. military aircraft trying to evacuate Americans from the city of Bor on Saturday, forcing the Ospreys - advanced helicopter-airplane hybrids - to abort their mission. On Sunday, the U.S. evacuated Americans by civilian U.S. and U.N. 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.

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

South Sudan forces are advancing toward Bor, the capital of Jonglei state, but have not yet confronted forces that defected and pledged allegiance to the former vice president, said South Sudan military spokesman Col. Philip Aguer.

New fighting was reported Sunday night in Upper Nile, one of South Sudan's two oil-rich states. Warrior Security, a private company, reported on Monday the deaths of 20 people in Nasir County in a dispute involving Machar supporters. Doctors Without Borders said it received 24 gunshot victims at its medical facility.

Aguer said elsewhere in the state civilians who had been told their relatives were killed in Juba tried to mete out mob justice. Warrior Security said ethnic Dinkas were attacked and killed. Aguer said he did not have a death toll.

Analysts have suggested that a tribal militia known as the White Army - from the Nuer ethnic group - is moving toward Bor, which is populated by Dinkas. Lanzer said he couldn't say anything with precision about those reports. Aguer said he has no confirmation on militia movements but that community leaders are trying to persuade the Nuer not to become involved.

"Everybody knows that Bor is a strategic location," Lanzer 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," the reason the U.N. is fortifying its position there.

The central government acknowledged on Sunday it has lost control of Bentiu, the capital of Unity, and the surrounding oil fields. Oil fields in the country's Upper Nile state are still controlled by the central government, Aguer said.

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 Navy SEALs were wounded in the evacuation attempt Saturday.

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.

On Monday, a Pentagon spokesman said the U.S. has moved additional Marines and aircraft from Spain to the Horn of Africa to provide embassy security and help with evacuations from South Sudan. Army Col. Steve Warren said the commander in Africa is getting the forces ready for any request that may come from the U.S. State Department.

A defense official said the extra forces moved to Djibouti will bring the total U.S. troops in the region to 150, with 10 aircraft, including Osprey helicopters and C-130 transport planes. Djibouti is the site of the only permanent U.S. military base in Africa.

The defense official was not authorized to speak publicly so spoke on condition of anonymity.

---

Associated Press Writers Edith M. Lederer at the United Nations and Pauline Jelinek and Lolita C. Baldor in Washington contributed to this report.