He said Manila would not "break or abrogate existing treaties", suggesting he wants to maintain the Philippines' ties with the US.
It comes days after Manila announced it was suspending annual joint military exercises with the US.
Relations between the old allies have become strained in recent months.
Washington has voiced concerns over the newly-elected president's "war on drugs", which has left more than 3,500 people dead in a matter of months. Mr Duterte has called President Barack Obama a "son of a whore".
Mr Duterte, who is visiting Beijing next week, has previously suggested China and Russia could be possibly alternate partners.
But while Mr Duterte reiterated in his latest speech that the traditional joint exercises with US troops would be stopped, he said he would not break the mutual-defence treaty entirely.
``I insist that we realign, that there will be no more exercises next year," he said.
He added: "We need not really break or abrogate our existing treaties because they say that it could provide us with the umbrella.
"We will maintain all military alliances because they say we need it for our defence." He did not explain who he meant by "they".

The 35-year-old threw a new F51 European record of 17.68m to score 1100 points and finish ahead of team-mates Josie Pearson and Gemma Prescott.
It beat the previous best of 15.83 set by Ireland's Catherine O'Neill in 2001.
"I'm throwing well at the moment and once I got the big throw, I knew the pressure was off," said Butterfield.
The Glasgow-based newcomer, who was left paralysed by a tumour on her spinal cord in 2011,  took up athletics earlier this year via the talent identification programme Girls4Gold after playing wheelchair rugby for a couple of years.
"Because I was already doing rugby and the strength and conditioning work with that, I just had to try to adapt that to athletics," she told BBC Sport. "I've loved it and trained hard but I know I have a lot more to learn.
"Representing GB for the first time here has been a bit surreal but the team has been great and everyone has been really welcoming.
"The difference sport has made to me is huge but I never dreamed I would be part of this so soon."
Compatriot Pearson was frustrated after three of her six throws were deemed to be fouls.
"There was a technical issue with my throws with an official saying I was breaking some of the rules," she said.
"I've been throwing the same way all season and not been pulled up on it before so it is frustrating for this to happen at a major championship where I know I could have thrown further."

Well, for many people Nick Griffin was the BNP, and his personal - and his party's - fortunes appeared intertwined.
He was its leader for 15 controversial years, in which he saw off criminal charges of racial hatred, and, for a moment, looked like he was on the verge of a breakthrough for a far-right leader.
There was the prospect of becoming a British Jean-Marie Le Pen.
In 2009 he and his then colleague Andrew Brons were elected to the European Parliament on an anti-immigration platform.
I was in Manchester Town Hall when the result of his election as an MEP for North West England was declared - he was surrounded by a large entourage which proceeded triumphantly through the building as he was being criticised from the podium by the other parties' candidates - including UKIP.
He later blamed that party for contributing to the BNP's electoral decline when it transpired that 2009 wasn't a turning point, but the high point, in his party's fortunes.
2014 hasn't been a good year for Nick Griffin.
He lost his seat in the European Parliament, was declared bankrupt, replaced as party leader and has now been expelled from the party.
He says he will not '"resort to the BBC gutter" to air his grievances - the members will sort it all out, he says.
But a political comeback looks like a very tall order.
President Rodrigo Duterte says the Philippines will not end alliances with other countries, despite his increasingly anti-US rhetoric.
[NEXT_CONCEPT]
Debutant Jo Butterfield led a British clean sweep of the medals in the women's F32/51 club throw at the IPC Athletics European Championships.
[NEXT_CONCEPT]
Why the fuss over the internal machinations of a party which has no MPs, no MEPs - and which polls suggest commands the support of about one per cent of voters?