The US State Department expressed support for the universal right to peaceful protests and reaffirmed its security commitment to South Korea as a corruption scandal involving President Park Geun-hye sparked weeks of nationwide rallies demanding her resignation.

"We have seen the press reporting of the political protests, and I would let the protesters and the government of Korea speak to that. You know where we stand on the right of peaceful protest and assembly and we continue to support that around the world," State Department spokesman John Kirby said at a briefing.

"People should have the ability to go out and voice their concerns about government. But it doesn't change one iota of our commitment to South Korea, to the government, to the people there, and to making sure that we continue to meet all our alliance commitments," he said.

Kirby said Korea remains "a steadfast ally, friend, and partner," and the US commitment to it is firm.

"It's a democracy and that's how democracies work. And people have that right and that ability and they're exercising that right. And I think that's important," he said.

South Koreans have taken to the streets in recent weeks, demanding Park step down over the scandal that centers on allegations that a long-time confidante of hers, Choi Soon-sil, exercised huge influence over her as well as state affairs, while extorting millions of dollars from big businesses.

Park has apologized to the nation twice, but has failed to calm the anger down. (Yonhap)