Secretary of State Rex Tillerson says there's no "hard evidence" of Russian involvement in Syria's chemical bomb attack, but charges Moscow's been "incompetent" and "out-maneuvered" by Bashar al-Assad.

In an interview with ABC News' "This Week" aired Sunday, Tillerson said in his visit to Russia this week, he'll call upon Moscow "to fulfill the obligation it made to the international community when it agreed to be the guarantor of the elimination of the chemical weapons."

"Why Russia has not been able to achieve that is unclear to me," he said. "I don't draw conclusions of complicity at all. But clearly, they've been incompetent, and perhaps they've just simply been out-maneuvered by the Syrians."

Also in the interview, Tillerson said there's been "no change" to the U.S. military stance in Syria beyond the missile strike in retaliation for the Assad government's use of chemical weapons on its citizens, yet the action carries a message for other countries acting outside international norms.

The U.S. still hopes to shepherd a "political process that we believe the Syrian people will lawfully be able to decide the fate of Assad," Tillerson said in reference to Syria's president.

This week's airstrike "was a message to Bashar al-Assad that your multiple violations of your agreements at the UN, your agreements under the chemical weapons charter back in 2013, that those would not go without a response in the future," he said.

If President Donald Trump needs to do more in Syria "he will do more,'' U.S. Ambassador to the United Nations Nikki Haley said on CNN's "State of the Union." Haley said she doesn't see a political solution in Syria with Assad remaining as president, but that other U.S. priorities were defeating Islamic State and to "get the Iranian influence out.''

On CBS News' "Face the Nation," Tillerson also said that the first priority for the U.S. remains defeating Islamic State.

"Once the ISIS threat has been reduced or eliminated, I think we can turn our attention directly to stabilizing the situation in Syria," he said, using an acronym for the jihadist group.

Tillerson conceded that removing Assad from power could "ultimately" require greater pressure, including military action, from the U.S. or an international coalition, but he said that isn't the preferred choice.

Libya Example

"We've seen what that looks like, when you undertake a violent regime change in Libya, and the situation in Libya continues to be very chaotic," he said. "We have to learn the lessons of the past and learn the lessons of what went wrong in Libya when you choose that pathway of regime change."

In the wide-ranging ABC interview, Tillerson also said the U.S. has "no objective" to change North Korea's regime as Kim Jong Un continues to ramp up Pyongyang's nuclear program, and that there's no reason for the U.S. to lift sanctions placed on Russia following its annexation of Crimea in 2014.

Even so, Tillerson said, without naming North Korea, that "if you violate international agreements, if you fail to live up to commitments, if you become a threat to others, at some point a response is likely to be undertaken."

Tillerson is heading to Lucca, Italy, for a two-day meeting of G7 foreign ministers that starts Monday, and he will continue from there to Moscow for meetings with Sergey Lavrov, his Russian counterpart, and other Russian officials.

Russia's Failure

Presslimination of the chemical weapons and why Russia has not been able to achieve that is unclear to me," Tillerson added.

Moscow has said it doesn't believe Assad's forces carried out the attack on Thursday that involved children and called for a "thorough and impartial" investigation.

Until Sunday, Tillerson, 65, the former chief executive of oil giant Exxon Mobil, hadn't done the talk-show circuit and had consented to few interviews since being sworn in as the top U.S. diplomat in February.

On North Korea's nuclear capability, Tillerson said Kim Jong Un "has made significant advancements in delivery systems, and that is what concerns us the most."

The U.S. has been "quite clear with the regime in Pyongyang" that it needs to cease all weapons testing "before we can think about having further talks with them," he said.

Tillerson said he will continue to press Russia on its meddling in last year's U.S. presidential election through hacking and leaking Democrats' emails, which U.S. intelligence agencies have concluded was ultimately aimed at helping Trump win the White House.

"We will continue to talk with them about how this undermines any hope of improving relations, not just with the United States, but it's -- it's pretty evident that they are taking similar tactics into electoral processes throughout Europe and so they're really undermining any hope for improved relations with many European countries as well," he said.