United States Secretary of State Mike Pompeo acknowledged on Tuesday that the militant Islamic State (IS) is gaining strength in some areas, but said the militant group's capacity to conduct attacks has been greatly diminished.

"It's complicated. There are certainly places where IS is more powerful today than they were three or four years ago,” Pompeo said in an interview with CBS This Morning. But he said the group's self-proclaimed caliphate is gone and its attack capability has been made much more difficult.

Pompeo was asked about a New York Times report that the militant group was gaining new strength in Iraq and Syria.

President Donald Trump said in December that US troops succeeded in their mission to defeat IS in Syria and were no longer needed in the country.

“We won,” he said at the time.

Pompeo, in his interview today, said the plan to defeat IS in the region was executed with 80 other countries and was very successful.

However, he cautioned that there is always risk that there will be a resurgence of “radical Islamic terrorist groups,” including al Qaeda and IS.

IS claimed responsibility for a wedding suicide attack that killed 63 people and wounded 182 on Saturday in the Afghan capital of Kabul.

US 'acting with wisdom' in Iran rift

The US state secretary also commented on the ongoing tensions with Iran, insisting that Washington was "acting with wisdom".

"It's wisdom to have withdrawn from the JCPOA (Joint Comprehensive Plan of Action), which was going to put Iran on the path to a nuclear weapon, and President Trump is determined not to let that happen."

Last year, President Trump had withdrawn US from the JCPOA, commonly referred to as the Iran deal, which had been a major foreign policy achievement of his predecessor, Barack Obama. Britain, France, Germany, China and Russia, who are also signatories of the deal, have urged the US administration to reconsider its move.

In another interview to Fox News Channel earlier today, Pompeo said that it was unfortunate an Iranian oil tanker detained off Gibraltar had been allowed to leave.

“It's unfortunate that that happened,” Pompeo said.

He added that if Iran is successful in making profit from the tanker's oil cargo, its Islamic Revolutionary Guard Corps will have "more money, more wealth, more resources to continue their terror campaign".

North Korea talks haven't resumed as quickly as hoped

Pompeo, in his interview to CBS, also talked about North Korea and admitted that US has not returned to the negotiation table with Pyongyang as quickly as it had hoped.

He added that Washington knew there would be 'bumps on the road' in the denuclearisation talks.

Speaking to CBS, Pompeo said Washington was concerned about North Korea's firing of short-range missiles.

"I wish they would not," he said, referring to the tests.

The latest of the missile tests by North Korea was carried out on Friday as Pyongyang fired two more short-range projectiles into the sea off its east coast.

The launches have complicated attempts to restart talks between US and North Korean negotiators over the future of Pyongyang's nuclear weapons and ballistic missile programmes.

Those denuclearisation talks have been stalled despite a commitment to revive them that was made at a June 30 meeting between US President Donald Trump and North Korean leader Kim Jong Un.

Pompeo further said that Stephen Biegun, US special envoy for North Korea, would be in the region on Tuesday and Wednesday but did not elaborate on the details of his trip. The State Department said last week that Biegun would travel to Japan and Seoul this week.

No 'mixed messages' on Huawei

In another interview with CNBC on Tuesday, Pompeo said that Washington was not sending “mixed messages” on Huawei Technologies and he does not believe a US blacklist of the Chinese telecommunications giant will block a trade deal with Beijing.

“I don't think there's a mixed message at all,” Pompeo said.

“The threat of having Chinese telecoms systems inside of American networks or inside of networks around the world presents an enormous risk, a national security risk,” he said.

Asked if Chinese President Xi Jinping was stalling negotiations because of US actions toward Huawei, Pompeo said: “That's not been our experience. That is not what's happening today.”

"I think he's prepared to engage in a complex set of trade negotiations,” Pompeo told CNBC. “So, no, he hasn't walked away, he hasn't said 'I won't talk if you do these things'."

Washington had blacklisted Huawei in May, alleging the Chinese company is involved in activities contrary to US national security or foreign policy interests.

US extended a reprieve that permits Huawei to buy components from American companies to supply existing customers, the Commerce Department said on Monday, but it also moved to add more than 40 of Huawei's units to its economic blacklist.

President Donald Trump, however, indicated over the weekend there would be no extension, saying what would happen would be the “opposite".

“Were actually open not to doing business with them, Trump said on Sunday. Huawei, the world's largest telecommunications equipment maker, is still prohibited from buying American parts and components to manufacture new products without additional special licenses.

The Huawei dispute coincides with a trade war between the world's two largest economies. Talks are at a standstill for now, with the threat of greater tariffs and other trade restrictions hanging over the world economy.