President Obama on Friday warned that tougher sanctions might be needed against North Korea amid worries that Pyongyang might conduct another nuclear test.

Speaking at a joint press conference with South Korean President Park Geun-Hye in Seoul, Obama said the two leaders were united in their approach to North Korea ahead of likely “further provocative actions.”

“It's important for us to look at additional ways to apply pressure on North Korea, further sanctions that have even more bite, as well as highlighting some of the human rights violations that make North Korea probably the worst human rights violator in the world,” said the president.

Obama's stop in South Korea comes during a week-long trip to four Asian countries and amid concerns that Pyongyang has stepped up activity at a nuclear installation.

The White House has said it is “closely” monitoring Pyongyang's activities and urged the country to avoid steps that would raise tensions on the Korean peninsula.

Obama said that North Korea’s behavior posed a “direct threat” not only to key allies in the region but to the U.S. as well.

“Some of the missile technology that’s being developed, the nuclear weapons that are being developed in North Korea, when matched up with a thoroughly irresponsible foreign policy and a provocative approach by the North Korean regime, poses a threat to the United States,” he said.

“And so we can’t waver in our attention,” Obama continued. “We have to make sure that in strong concert with our allies, that we are continuing to press on North Korea to change its approach.”

The regime in Pyongyang has often used nuclear tests or missile launches to gain attention and launch talks but Obama said the U.S. would not “reward bad behavior.”

“We don’t go through a constant cycle in which provocative actions by North Korea result in dialogue that leads nowhere and concessions to the North Koreans,” he vowed.