"There is obviously participation by people, organisations from outside of Hong Kong, in politics in Hong Kong, over a long time," Leung Chun-ying, Hong Kong's chief executive, said during a TV interview on Sunday.
Leung refused to reveal which countries were behind the alleged interference. He also said that the movement is now "out of control even for people who started it, for people who planned it, for people who scripted it".
Dozens of people, including 22 police officers, were reportedly injured in two nights of clashes that began late on Friday in the densely populated Mong Kok district. Four people were arrested early on Sunday, police said.
The area was calm early on Monday, although scores of protesters remained on the streets. Hopes of easing the worst political crisis in Hong Kong since the UK handed the colony back to China in 1997 rest on talks scheduled for Tuesday between the government and student protest leaders that will be broadcast live.
The demonstrators first took to the streets in late September in opposition to the Chinese central government's decision to screen candidates running in the territory's first direct elections, due to be held in 2017.