Tough U.N. sanctions are putting pressure on North Korea to halt its nuclear program, the U.S. ambassador to the United Nations said Tuesday.

Susan Rice said in an interview with The Associated Press and APTN on Tuesday that North Korea is indicating in various ways that it is feeling the pressure of sanctions "and perhaps responding to it." She declined to elaborate on Pyongyang's response.

"North Korea sanctions, which are now the toughest sanctions on the books against any country in the world today, ... have been actively and forcibly implemented by member states all over the world," she said. "So North Korea is feeling far greater pressure to halt its nuclear weapons program than it has in the past."

The U.N. Security Council imposed new sanctions against North Korea in June, banning all arms exports after the communist regime conducted a second nuclear test and test-fired missiles. The impoverished nation is believed to earn hundreds of millions of dollars every year by selling missiles, missile parts and other weapons to countries such as Iran, Syria and Myanmar.

The new sanctions also authorized ship searches on the high seas, ordered an asset freeze and travel ban on companies and individuals involved in the country's nuclear and weapons programs, and called on all nations to prevent financial institutions or individuals from providing financing for any activities related to the country's banned weapons programs.

The first North Korean ship to be monitored under the U.N. resolution turned back before reaching port in July, possibly in Myanmar, with a suspected illicit cargo of weapons. In August, the United Arab Emirates said it found banned North Korean weapons, including rocket-propelled grenades, headed for Iran on an Australian-owned, Bahamas-flagged cargo ship. And on Dec. 12, authorities in Thailand, acting on a U.S. tip, seized an aircraft with 35 tons of North Korean weapons which arms trafficking researchers say was headed for Iran.

When U.S. Ambassador Stephen Bosworth, the special U.S. envoy to North Korea, visited Pyongyang earlier this month he said the North lobbied to have the sanctions eased. But Bosworth said that wouldn't happen until North Korea came back to nuclear negotiations and made significant progress on getting rid of its atomic weapons.

Both Washington and Pyongyang agreed on the need to resume the stalled six-party talks but the North did not make a firm commitment on when it would rejoin the negotiations with the U.S., Russia, China, South Korea and Japan.

Rice stressed that Bosworth's visit to Pyongyang was not to open bilateral U.S.-North Korean negotiations — which the North has been seeking — but to state very clearly that President Barack Obama's administration expects the country to return to the six-party talks.

The talks began in 2003, and in 2005 there was agreement on a disarmament pact which calls for North Korea to end its nuclear programs in exchange for economic aid, security assurances and diplomatic recognition.

"We're not interested in talks for the sake of talks, but verifiable and irreversible steps" to implement the 2005 agreement, Rice said.

Last week, Chinese Vice President Xi Jinping, a rising star in the country's leadership, called for efforts to quickly resume the talks, which Beijing hosts. He also said China wants to work closely with South Korea to advance the denuclearization process on the Korean peninsula.

Asked about a report that the six-party talks may resume in February, Rice said, "I'm not prepared to share what the timing of that will be but we've certainly indicated our readiness..."

"I think ambassador Bosworth aptly characterized the talks when he came back," she said. "They were productive and constructive, but it remains to be seen what comes next."