WASHINGTON (REUTERS) - US officials are doing their best to ignore Philippines President Rodrigo Duterte's hostile rhetoric and taking comfort in the fact that he has yet to translate his words into less military cooperation.

The United States is trying not to give the new president a pretext for further outbursts while at the same time pressing ahead with military and other cooperation at lower levels, US officials said on Monday (Oct 3).

One US official said that while the Obama administration is more worried about Mr Duterte that it is letting on publicly, there is no great concern about the defence implications of a political break because the United States has alternatives.

The official, who spoke on condition of anonymity, said these include the Navy Region Centre Singapore, training facilities in Brunei, and the possibility of greater naval access in Vietnam.

While an open break with Manila would create problems in a region where China has grown increasingly aggressive, there are no serious discussions about taking punitive steps such as cutting aid to the Philippines, according to two US officials.

Mindful of anti-colonial sentiment, despite the estimated 3 million people of Philippine descent living in the United States, US officials do not want to say or do anything that might encourage Mr Duterte to turn his rhetoric into reality.

"He is like Mr Trump," a senior South-east Asian official said, referring to US Republican presidential nominee Donald Trump. "He craves attention, and the more he gets, the more outrageous he becomes. It is wisest to ignore him."

Asked by a reporter for his response to that comment, presidential spokesman Ernesto Abella said: "That is their opinion."

In the last month, Mr Duterte has called US President Barack Obama a "son of a whore", leading the White House to cancel a planned meeting.

He also appeared to liken himself to Hitler and said he would "be happy" to kill 3 million drug users and peddlers in the country but later apologised to the Jewish community for his reference to the Holocaust.

Mr Duterte also said his mention of the Nazi leader was a reference to how his critics had portrayed him.

In his latest broadside, Mr Duterte said on Sunday (Oct 2) he got expressions of support from Russian Prime Minister Dmitry Medvedev and from an unnamed Chinese official after he complained of ill-treatment by Washington.

While Mr Duterte has publicly suggested he would end joint military exercises, push US special operations forces out of the southern Philippines, and review a defence pact signed two years ago, US officials stressed none of this has happened.

US military officials said they were well aware of Mr Duterte's comments, but their counterparts in the Philippines had reassured them that business continues as usual.

"No one is really losing sleep over it," said one US defense official on condition of anonymity. "It is all bluster," said a second defence official, saying Mr Duterte's remarks "have not bled over into our world".

There are about 100 US soldiers in Zamboanga City in the south, a Philippine military spokesman said, well below the 1,200 US forces initially deployed to help train and advise local troops fight the Abu Sayyaf Group, an Islamist militant group.

The Philippine military spokesman said he was not aware of any plan to pull them out.

Other than Japan's 1942-1945 occupation, the United States effectively ruled the Philippines from 1898, when it acquired the island chain from Spain following the Spanish-American War, until recognising its independence in 1946.

The two nations signed a mutual defence treaty in 1951, but their close cooperation diminished a quarter century ago, when the Philippines kicked US forces out of two large military installations, including the naval base at Subic Bay.

Two years ago, however, the two signed the Enhanced Defence Cooperation Agreement (EDCA), which allows US troops to build storage facilities for maritime security and humanitarian and disaster response operations.

Under the agreement, two C-130 transport planes and 100 US servicemen have been at an air base in the central Philippines since Sept 25. On Tuesday, the two countries launched PHILBEX, an eight-day joint marine exercise.

Commander Gary Ross, a Pentagon spokesman, said the EDCA is an international agreement, and the United States and Philippines are bound by international law. Citing the agreement's text, Commander Ross said it has an initial term of 10 years, after which either side may end it with a year's written notice.

The former colony is a key element of the Obama administration's policy of "rebalancing" its foreign policy toward Asia, and the two nations have begun joint patrols in the South China Sea as China asserts its territorial claims.

China claims 90 per cent of the South China Sea, which is believed to be rich in oil and gas, its claims overlapping with those of the Philippines, Brunei, Malaysia, Vietnam and Taiwan.

US officials are disturbed by the fact that more than 3,100 people have been killed since Mr Duterte took office three months ago and launched a promised drugs war, yet they value the country's long-standing military ties.

"Sometimes you have to hold your nose about the individuals and deal with the countries. The United States doesn't have the luxury of writing off the Philippines, so we have to find a way to deal with this extraordinarily distasteful leader while still conveying our opposition to his human rights policies," said Mr Frank Jannuzi, a former Senate Foreign Relations Committee Asia specialist now at the Maureen and Mike Mansfield Foundation.

US lawmakers have conveyed their concerns in repeated conversations with the Philippine Embassy, where diplomats are torn between their need to represent Mr Duterte's government and their concerns about what he has been saying.

The United States has sent the Philippines hundreds of millions of dollars in foreign aid and military and development assistance in recent years, making it the third-largest Asian recipient of US military aid after Afghanistan and Pakistan.

Two influential senators, Mr Ben Cardin, the top Democrat on the Senate Foreign Relations Committee, and Mr Patrick Leahy, the top Democrat on the sub-committee that handles foreign aid, said Congress would take Mr Duterte's policies into account when deciding on aid for the current fiscal year.