U.S. President Barack Obama slapped North Korea with more stringent sanctions Thursday for defying the world and pushing forward with its nuclear weapons program, weeks after it launched a satellite-carrying rocket into space and conducted its fourth underground nuclear test.

Both actions led to worldwide condemnation of the reclusive country and fuelled fears that it continues to move toward building an atomic arsenal.

Democratic and Republican lawmakers, many of whom say Obama hasn't been tough enough on North Korea, overwhelmingly approved the bill last week and sent it to the White House. The House voted 408-2, following a unanimous vote by the Senate.

Obama signed the legislation away from the news media and issued no statement. Up until Wednesday, the administration had said it didn't oppose the bill but declined to say whether Obama would sign it into law.

The expanded sanctions are being imposed as the U.S. and China are in delicate negotiations over a UN Security Council resolution on new sanctions. China, which is North Korea's most important ally, has raised concerns about measures that could devastate North Korea's economy.

The new measures are intended to deny North Korea the money it needs to develop miniaturized warheads and the long-range missiles required to deliver them.

$50 million authorized

The legislation also authorizes $50 million over the next five years to transmit radio broadcasts into North Korea, purchase communications equipment and support humanitarian assistance programs.

"This is an authoritarian regime. It's provocative. It has repeatedly violated UN resolutions, tested and produced nuclear weapons, and now they are trying to perfect their missile launch system," Obama said in an interview broadcast by CBS This Morning after North Korea launched the long-range rocket.

Senator Bob Menendez, a New Jersey Democrat and sponsor of the bill, said he hoped the UN Security Council and China, in particular, will "take notice of this strong showing of U.S. leadership" and work to put in place similar measures.

'One clear message'

"Let's stand together with a single voice and one clear message: Any provocation will be met with consequences that will shake the Kim regime to its foundations," Menendez said.

Obama consulted with Chinese President Xi Jinping after the Jan. 6 nuclear test, and with the leaders of Japan and South Korea after the rocket launch to reaffirm the U.S. commitment to their security. The U.S. has also opened talks with South Korea about developing more missile-defence systems to eliminate the possibility that a North Korean missile could reach U.S. facilities.

Japan announced new sanctions last week that include expanded restrictions on travel between the two countries and a complete ban on visits by North Korean ships to Japan.

South Korea cut off power and water supplies to a factory park in North Korea, a day after the North deported all South Korean workers there and ordered a military takeover of the complex that had been the last major symbol of cooperation between the rivals.