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".
President Rodrigo Duterte says the Philippines will not end alliances with other countries, despite his increasingly anti-US rhetoric.