Philippines President Rodrigo Duterte sought to defuse a row with the United States on Tuesday, voicing regret for calling President Barack Obama a "son of a bitch", a comment that prompted Washington to call off a bilateral meeting.
The tiff between the two allies overshadowed the opening of a summit of East and Southeast Asian nations in Vientiane, Laos.
It also soured Obama's last swing as president through a region he has tried to make a focus of U.S. foreign policy, a strategy widely seen as a response to China's economic and military muscle-flexing.
Diplomats say strains with longtime ally the Philippines could compound Washington's difficulties in forging a united front with Southeast Asian partners on the geostrategic jostle with Beijing over the South China Sea.
Duterte has bristled repeatedly at criticism over his "war on drugs", which has killed about 2,400 people since he took office two months ago, and on Monday said it would be "rude" for Obama to raise the question of human rights when they met.
Such a conversation, Duterte told reporters, would prompt him to curse at Obama, using a Filipino phrase "putang ina" which can mean "son of a bitch" or "son of a whore".
He has previously used the epithet against Pope Francis, although he later apologized, and the U.S. ambassador to the Philippines.
After Washington called off Tuesday's bilateral meeting between Obama and Duterte in response to his latest comment, the Philippines issued two statements expressing regret and also briefed reporters.
"President Duterte explained that the press reports that President Obama would 'lecture' him on extrajudicial killings led to his strong comments, which in turn elicited concern," the Philippines government said in a statement.
"He regrets that his remarks to the press have caused much controversy," it added. "He expressed his deep regard and affinity for President Obama and for the enduring partnership between our nations."
Obama's deputy national security adviser, Ben Rhodes, said the focus on Duterte's comments leading into the summit had not created a constructive environment for a bilateral meeting.
"All of the attention frankly was on those comments, and therefore not on the very substantive agenda that we have with the Philippines," he told reporters.
Officials from both countries said there would be no formal meeting rescheduled in Laos but a short conversation between the two presidents was possible.
Instead of the Duterte meeting, Obama held talks with South Korean President Park Geun-hye, a day after North Korea fired three medium-range missiles into the sea. He urged a full implementation of sanctions against North Korea, adding that the missile test demonstrated the threat that Pyongyang posed
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