(CNN) -- New airstrikes have targeted a town in northwest Syria that was hit by a deadly chemical attack earlier this week, activists said.
It wasn't immediately clear who conducted the strikes on Khan Sheikhoun, which was hit on Friday and Saturday, though only Russian and Syrian regime aircraft have been bombing that area of rebel-held Idlib province.
The latest attacks follow a strike early Friday by the United States on a Syrian airbase. The US blames Syria for Tuesday's chemical attack, which left more than 85 people dead and hundreds more injured.
The new strikes came as Russia, the Syrian regime's main ally, sent a frigate armed with cruise missiles to a Syrian port in an apparent show of force in response to the US strike.
Key developments
The Syrian air force resumed flight operations at the base that the US had struck Friday. Pentagon probes possible Russia involvement in chemical attack that prompted US strike. US officials say about 20 planes were destroyed in Friday's attack on the Shayrat base. US ambassador to the UN Nikki Haley to UN says US 'prepared to do more' in Syria. Russian President Vladimir Putin said US strike was an "act of aggression."
At least one woman was killed and three other people injured in Saturday's strikes in Khan Sheikhoun, two activists in the town said. The strike that killed the woman happened in a residential neighborhood, activist Alaa Al-Youssef told CNN.
It wasn't clear where the strikes were launched from, but the Syrian air force resumed flight operations at the base that the US had struck Friday, two pro-regime media outlets and an opposition group said Saturday.
A US defense official said Friday's strikes were not intended to damage runways or fully disable the base. Instead, the strikes hit aircraft, fuel storage, weapons dumps and other equipment, aiming to send a message to the Syrian regime that any use of chemical weapons would not be tolerated, the official said.
In the aftermath of the US strike, Russia pledged to help strengthen Syria's air defenses. Russian state media reported that a frigate, the Admiral Grigorovich, would call at a logistics base at Tartus, Syria. It had earlier picked up supplies at the Black Sea port of Novorossiysk.
NATO called it one of the largest deployments from Russia in decades.
Retired US Lt. Gen. Mark Hertling, a CNN military analyst, said the frigate appeared to be a show of force by Russia, which since late 2015 has been conducting airstrikes in Syria against forces opposing the Syrian regime.
"I think the Russians were caught off guard (by the US strikes)," Hertling said. "So they want to make sure they're tracking those (US) ships."
US quiet on next steps
The White House late Friday refused to say whether its strike on Shayrat airbase was a one-off action or part of a new strategy designed to hobble the military capabilities of President Bashar al-Assad. Nor would it say whether the US believed Assad should step down after the chemical attack on Khan Sheikhoun that killed at least 80 people and injured dozens more on Tuesday.
The White House refused to discuss next steps. Press Secretary Sean Spicer said President Donald Trump would not "telegraph his next move." Speaking to reporters at Trump's Mar-a-Lago resort in Florida, Spicer said the US missile attack was "very decisive, justified and proportional."
He declined to say whether Trump now believed Assad should relinquish power. "First and foremost the President believes that the Syrian government [and the] Assad regime should abide by the agreement they made not to use chemical weapons," Spicer said.
US Secretary of State Rex Tillerson said Russia had failed to honor an agreement to to guarantee the elimination of Syria's chemical weapons. "Clearly, Russia has failed in its responsibility to deliver on that commitment from 2013, he said. "So either Russia has been complicit or Russia has been simply incompetent in its ability to deliver on its end of that agreement."
British Foreign Secretary Boris Johnson, meanwhile, canceled his planned Monday visit to Moscow, citing developments in Syria.
In a statement Saturday, Johnson said his priority was to continue contact with the US and others in the run-up to a meeting of G7 foreign ministers in Italy on Monday and Tuesday, with the aim of building "coordinated international support for a ceasefire on the ground and an intensified political process."
Russia complicit?
US officials have said the Pentagon is looking for any evidence that the Russian government knew about or was complicit in Tuesday's chemical attack.
A US military official told CNN the Pentagon was examining specifically whether a Russian warplane had bombed a hospital in Khan Sheikhoun five hours after the initial chemical attack, with the aim of destroying evidence.
Russia flatly denies the allegations.
Trump said he ordered the airstrike on the Shayrat base because the US believed aircraft that carried out the chemical attack were launched from there.
Russian President Vladimir Putin denounced the US strike as "act of aggression" and said it violated international law.
Russian Senator Alexey Pushkov said that the disappointment was "mutual" and suggested that Tillerson's comments were made to gain "leverage" in upcoming US-Russia talks. Tillerson is due to meet Russian Foreign Minister Sergey Lavrov in Moscow next week.
He said on Twitter that the "conditions for negotiations in Moscow were even worse than (former Secretary of State John) Kerry's times."
US Ambassador to the United Nations Nikki Haley warned Friday that the United States "is prepared to do more" in response to Syria's use of chemical weapons and delivered a sharp rebuke to Russia for its support of the Syrian regime.
"Every time Assad has crossed the line of human decency, Russia has stood beside him," Haley told the council. Russia "bears considerable responsibility" for Assad's use of chemical weapons, she said.
