WASHINGTON — The Trump administration plans to impose new sanctions against Russia on Monday to punish it for enabling Syria’s use of chemical weapons in its civil war, the latest in a series of actions by both sides underscoring the deterioration in relations between Moscow and the West.
The sanctions, coming shortly after US-led airstrikes against facilities linked to Syria’s chemical weapons, are meant to signal that the United States holds responsible not just the Damascus government of President Bashar Assad but also his patrons in Russia and Iran.
President Trump has vowed that Syria’s allies will pay a “big price” for permitting his use of poison gas.
The sanctions were announced Sunday by Nikki R. Haley, the US ambassador to the United Nations and the administration’s leading public voice excoriating Russia in recent days.
“They will go directly to any sort of companies that were dealing with equipment related to Assad and chemical weapons use,” she said on CBS’s “Face the Nation.” “And so I think everyone is going to feel it at this point. I think everyone knows that we sent a strong message and our hope is that they listen to it.”
On Sunday, Trump defended his use of the phrase ‘‘mission accomplished’’ to describe the missile strikes. In an early-morning tweet, he said the strikes were ‘‘perfectly carried out’’ and that ‘‘the only way the fake news media could demean was by my use of the term ‘mission accomplished.’’’
He added that he knew the media would seize on the phrase but said it should be used often. ‘‘It is such a great military term, it should be brought back,’’ he wrote. His choice of words recalled a similar claim made by President George W. Bush in 2003 after the US-led invasion of Iraq.
Trump has tried through most of his presidency to forge a friendship with President Vladimir Putin of Russia and avoid criticizing him personally even as a special counsel, Robert Mueller, investigated whether the Trump campaign coordinated with Russia during the 2016 election.
But in recent weeks, Trump’s administration has intensified actions against Russia, and the president singled out Putin over Syria’s use of chemical weapons on Twitter and again in a televised speech Friday night.
New sanctions Monday would be the third round imposed by the Trump administration against Russia in the past four weeks.
Last month, the administration targeted Russian companies and individuals for intervening in the 2016 election and mounting cyberattacks against Western facilities. It followed that this month with penalties against Putin’s inner circle, singling out some of Russia’s richest men and top government officials.
The administration also expelled 60 Russian diplomats and intelligence officers and closed the Russian Consulate in Seattle in response to the poisoning of a former Russian spy living in Britain.
The strikes against Syria were in retaliation for a suspected chemical attack that killed more than 40 people in the Damascus suburb of Douma on April 7.
The allied mission was designed to avoid provoking Russia into a response. By hitting just three targets and limiting the attack to a single night, the Trump administration seemed to keep it limited enough not to compel Moscow to lash back.
But Haley said the administration was determined to make Moscow pay a price for supporting Assad, noting that it had vetoed six UN resolutions related to Syria and chemical weapons.
“Assad knew that Russia had its back,” she said on “Fox News Sunday.” “Assad knew that Russia would cover for him at the United Nations and Assad got reckless and he used it in a way that was far more aggressive.”
In a separate development Sunday, the leaders of Russia, Iran, and the Hezbollah group in Lebanon said that the missile strikes on their ally, Syria, have complicated prospects for a political settlement to the war.
Assad appeared briefly on state TV, seemingly unfazed by the military action — and even reportedly in high spirits, the Associated Press reported
Assad told a group of visiting Russian lawmakers that the strikes were accompanied by a campaign of ‘‘lies and misinformation’’ against Syria and Russia in the UN Security Council.
Moscow and Damascus are waging the same ‘‘battles’’ against terrorism and ‘‘to protect international law based on respect of the sovereignty of countries and the wills of people,’’ Assad said in comments carried by state media, an apparent jab at the three Western allies.
Russian lawmaker Dmitry Sablin, who met with Assad, said the Syria leader appeared upbeat and believed the airstrikes would unify the country.
Russia and Iran have called the US action a ‘‘military crime’’ and ‘‘act of aggression.’’ The Security Council on Saturday rejected a Russian resolution calling for condemnation of the ‘‘aggression’’ by the United States, France, and Britain.
Putin spoke by phone with Iranian President Hassan Rouhani, and they agreed the Western airstrikes were an ‘‘illegal action . . . adversely impacting prospects for political settlement in Syria,’’ the AP reported, citing a Kremlin statement.
Putin said the actions violated the UN Charter and if they continue, ‘‘it will inevitably entail chaos in international relations,’’ the statement said.
The official IRNA news agency quoted Rouhani as saying the United States and ‘‘some Western countries do not want Syria to reach permanent stability.’’
Hassan Nasrallah, the leader of Lebanon’s Hezbollah group, which has hundreds of fighters backing Assad’s forces, said the airstrikes failed to ‘‘terrorize or break the spirits’’ of Syria and its allies.
Instead, he said, the attack bolstered the confidence of the Syrian army and its allies and may sink the already-faltering UN-backed peace process on Syria in Geneva.
Marine Lieutenant General Kenneth F. McKenzie, director of the Joint Staff at the Pentagon, said the allied airstrikes ‘‘took out the heart’’ of Assad’s chemical weapons arsenal. However, he acknowledged that some portion of Assad’s chemical arms infrastructure was not targeted.
Assad denies he has used chemical weapons and said the United States has yet to present evidence of a chlorine gas attack on civilians in Douma. The United States says it suspects that sarin gas also was used.
A team from the Organization for the Prohibition of Chemical Weapons is in Syria to investigate the Douma incident and is due to visit the town. Syria regained full control of Douma on Saturday after a surrender deal with the rebels.