London (CNN)The United States, while working with Moscow on a ceasefire in Syria, understands that Russia's version of a political solution there "is not necessarily a workable equation," Secretary of State John Kerry told CNN's Christiane Amanpour in an exclusive interview on Tuesday.
Kerry: Russia's political solution in Syria may not be workable
"But," he told her, "we would not have gotten the initial ceasefire without Russia. And literally tens of thousands of lives were saved."
The United States and Russia announced Monday that they would work towards reviving February's ceasefire agreement, which has since disintegrated significantly.
The Syrian regime, for its part, announced Monday that the temporary truce in Aleppo would be extended for 48 hours, according to the country's state news agency, SANA. The Assad regime and the Russian military have been battling for months to retake Aleppo from opposition and extremist forces.
Amanpour had asked Kerry: "What is it that makes you believe that the Russians are your partners in trying to get a ceasefire and a political resolution when they're actually Assad's partner, certainly in trying to regain Aleppo for instance?"
"Is it perfect? No," Kerry said. "Are there still problems to work out? Yes. There's a five-year war, and it's really more than one war.
"You have Kurds versus Kurds, you have Kurds versus Turkey, you have Saudi Arabia and Iran, you have Sunni and Shiite, you have people again Daesh [ISIS] and people against Assad. I mean, this is a very complicated battlefield," he said.
"Russia has an interest in not being bogged down forever in Syria. Russia has an interest in not becoming the target of the entire Sunni world and having every jihadi in the region coming after Russia," he added.
"If Russia is going to avoid a morass in Syria altogether, they actually need to find a political solution."
The secretary of state acknowledged that any agreement reached on Syria is, ultimately, nothing more than "words on a paper."
But negotiations have at the very least set up a "mechanism" in which people with real influence on the ground can talk and coordinate, he said.
"The key is going to be enforcement. We're looking at other methods of enforcement beyond that. But we're not there yet, but we're building what I hope will be a stronger structure."
As Secretary Kerry wrangles with the war in Syria, one of his signature achievements -- a nuclear deal with Iran -- appears under threat.
Kerry's Iranian counterpart, Foreign Minister Javad Zarif, has suggested that the U.S. is not living up to its end of the agreement.
America is "imposing heavy penalties on people who wanted to do business with Iran," he told the New Yorker last month. "If one side does not comply with the agreement then the agreement will start to falter."
More than 100 members of Iran's parliament earlier this month said President Hassan Rouhani should stop implementing the nuclear deal because of America's alleged shortcomings.
The fear Iran says businesses have of doing business in their country, Kerry said, is "misplaced."
"The banks in Europe are free to lend, to back a deal, to open an account for Iran, to engage in commerce," he said.
Iran has "the rights to the benefits of a deal that they have agreed to. They have undone their centrifuges. They have lived by every component of this agreement."
He suggested, however, that some companies may cite fear of American regulation as an excuse not to do business with Iran.
"There's a lot at play here. We just ask people to call us, look at any particular agreement, and we will clarify for them if there's any doubt."