WASHINGTON – The United States on Sunday ordered non-emergency staff to leave Ivory Coast and warned Americans not to travel to the West African country, which is in the grip of growing post-election violence.

The US State Department also ordered relatives of its staffers to leave Ivory Coast, where at least 50 people have been killed in recent days.

The US government cited a "deteriorating political and security situation" and "growing anti-western sentiment" in the West African country.

"The State Department recommends that US citizens who are concerned about their safety take advantage of commercial means of transportation while they are available and while borders remain open," it added as tensions reached a boiling point in Ivory Coast, the world's biggest cocoa producer.

Both strongman Laurent Gbagbo and his rival Alassane Ouattara claim to have won last month's presidential vote. But while the latter has been recognized as the victor by the international community, the incumbent is doggedly clinging to power.

The US embassy's consular section in Abidjan, meanwhile, has "temporarily curtailed all consular services except emergency services for US citizens," the State Department added.

"Due to drawdown of consular staff, the embassy has diminishing ability to assist US citizens wishing to depart the country."

It added that "hostility against westerners, including US citizens, cannot be ruled out."

The State Department had authorized the departure of its non-emergency personnel and families on Thursday, but Sunday's statement marked the first such order.

The United Nations, United States, former colonial power France, the African Union and Ivory Coast's West African neighbors in the ECOWAS regional bloc have all demanded that Gbagbo step aside and allow Ouattara to assume office.

Instead, there is every sign that the regime is hardening its stance.

Gbagbo ordered the 10,000-strong UN mission to leave on Saturday, accusing it of arming rebels loyal to his rival Alassane Ouattara, but UN Secretary General Ban Ki-moon dismissed the ultimatum and urged him to step down.

The UN peacekeeping force's determination to stay threatens to provoke a showdown with Gbagbo's hardline supporters, but leaders of the world body said it would remain and investigate reports of death squad killings.

UN High Commissioner for Human Rights Navi Pillay expressed concern about "the growing evidence of massive violations of human rights" in the restive West African country since Thursday.

More than 200 other people have also been injured over the past three days, she said in a statement issued in Geneva, vowing "to ensure that perpetrators are held accountable for their actions."

The US embassy was damaged by an "errant" rocket-propelled grenade during Thursday's fighting.

Ivory Coast has been split since 2002, when a failed putsch against Gbagbo sparked civil war, but there has been a truce since 2003.