U.S. Secretary of State John Kerry urged North Korea on Monday to forgo any provocative actions, warning the U.S. is ready to impose even harsher sanctions than the latest U.N. resolution on the communist nation.

Kerry issued the warning at a news conference during a landmark visit to Hiroshima, Japan, amid concerns that Pyongyang could conduct another nuclear test, its fifth, ahead of the birthday of founding leader Kim Il-sung on Friday.

He said sentiment was uniform at a meeting of the foreign ministers of the so-called Group of Seven advanced economies.

"Every one of us expressed our concern about the North Korean provocative behavior in recent months," Kerry said, according to a transcript provided by his department. "And together, we issue a call on the DPRK to refrain from actions and rhetoric that further raises the tensions of the region, and instead, to take the necessary, concrete steps towards fulfilling its international commitments and obligations."

 Kerry said that "a few measures" were left out of the latest U.N. sanctions resolution, but could be enforced in the coming months "depending on what actions the North decides to take." He didn't elaborate on what those measures are, but they're believed to be sanctions deemed too tough for China to agree to.

"So it is still possible that we will ratchet up even more, depending on the actions of the DPRK," he said.

The U.N. sanctions are believed to be the harshest ever to be imposed on Pyongyang. The measures, among other things, require mandatory inspection of all cargo going into and out of the North, regardless of whether by land, sea or air, while banning its exports of coal, iron and other mineral resources.

"We now have stronger sanctions in place against the DPRK. In addition to that, we have moved to discussions about the potential deployment of THAAD (missile defense system), which is a defensive system, as well as other steps that we are engaged in with respect to North Korea," Kerry said. Despite the pressure, however, Kerry said that the U.S. is ready for peace talks with Pyongyang and to provide the impoverished nation with economic aid and other assistance, but the North must first demonstrate its commitment to give up nuclear programs.

"We are prepared to get back to talks. We have made it clear that we are prepared to negotiate a peace treaty on the peninsula.

We are prepared to negotiate a non-aggression agreement. We are prepared to actually provide economic assistance and welcome the North back to the community of nations," Kerry said.

"We're prepared to provide aid and we're prepared to work with our colleagues on development and the long-term future. We're prepared to work with South Korea on the concept of reunification, if that's what they want. But it all depends on the North making the decision that they will negotiate denuclearization," he said.

A senior State Department official, speaking on the condition of anonymity during a background briefing in Japan, said that the U.S. and other members of the six-party nuclear talks with the North are ready to honor a 2005 deal that calls for providing the North with normalization of relations, security guarantees and economic aid.

"But all of that was then and is now conditioned on North Korea moving irreversibly and credibly along the path of full denuclearization. And the sooner that North Korea comes face to face with that, the better for all concerned, including them," the official said, according to a State Department transcript.

The official also said that there is "a widespread belief" that the new U.N. sanctions "will start to bite on North Korea in a significant way over the coming weeks and months." He added that there is a "considerable amount of work underway about what further options could be deployed, either with or without additional North Korean provocations."

Kerry's visit to Hiroshima and the memorial to the city's atomic bombing was the first by a U.S. secretary of state. He said he believes "everyone should visit Hiroshima" and he hopes President Barack Obama will also do so.

Kerry also made a strong pitch for Obama's initiative for a nuclear-free world, and took a swipe at Republican presidential front-runner Donald Trump for suggesting that South Korea and Japan develop their own nuclear arsenal as a way to reduce U.S. security burdens.

"It is also why any suggestion by any candidate for high public office that we should be building more weapons and giving them to a country like Korea or Japan are absurd on their face and run counter to everything that every president, Republican or Democrat alike, has tried to achieve ever since World War II," he said.

North Korea, meanwhile, said the international community must remove sanctions before Pyongyang returns to the negotiation table.

"Dialogue and military threats, dialogue and sanctions can never go together. Such logic that the purpose of imposing sanctions is to have a dialogue can never work on the DPRK," North Korea's foreign ministry said Tuesday.

DPRK is the acronym of North Korea's official name -- the Democratic People's Republic of Korea.

"Some countries are talking about the six-party talks, simultaneous pushing forward of denuclearization and the conclusion of a peace treaty and the like. Even a mere child knows well that dialogue is impossible under the present tense situation on the peninsula," it added. (Yonhap)