The Russian military has reportedly gone on high alert in anticipation of a potential U.S. attack on the forces of Syrian President Bashar al-Assad, a Moscow ally accused of using chemical weapons in a seven-year civil war.

Leading Russian politicians and military officials reacted to President Donald Trump's promise Monday to respond "forcefully" within "the next 24 to 48 hours" to the Syrian military's alleged use of toxic gas earlier this week in rebel-held Douma, a suburb of Damascus.

Vladimir Shamanov, head of the lower parliamentary house's defense committee and a former airborne troops commander, said Russia had an obligation to protect its ally. Syria has denied the chemical weapons charges and has called for the U.S. to withdraw from the country.

Trending: Coachella 2018 Performers: New Artist Alina Baraz Wants To See Beyoncé and SZA, Too

Related: Russia says Syrian war getting 'too dangerous' as Trump decides if he will attack

"The politics of double standards have hit rock bottom. And here the United Russia party conscientiously states that all political, diplomatic and military measures if necessary will be taken. No illegal action will remain unanswered," Shamanov said, according to the state-run Tass news agency.

"They should not pin their hopes on their naval task forces and their deceptions. We are a sovereign country, and we have allies and guarantors for those events taking place in Syria. We won’t let the Americans hammer nails on someone else’s anvil," he added.

GettyImages-931207138

LOUAI BESHARA/AFP/Getty Images

Trump said Monday he "had a lot of options militarily" and would probably discuss a potential operation only "after the fact." Meanwhile, at least one U.S. guided missile destroyer was already near the Syrian coast on Tuesday, according to The Wall Street Journal, and a second, the USS Porter, could arrive sometime soon. U.S. Naval Forces Europe announced Tuesday that the USS Donald Cook had departed from nearby Cyprus, but did not say where it was headed.

Story continues

Don't miss: David Tennant Was 'Unprepared’ for the ‘Good Omens’ TV Show Fanbase

An Arleigh Burke-class guided missile destroyer, the Donald Cook is armed with Tomahawk cruise missiles, the same launched against a Syrian air base after reports of a deadly chemical weapons attack in rebel territory a year ago. An airstrike hit a Syrian air base in the central Homs province Sunday, but the Pentagon has denied responsibility for the attack, which killed Iranian and Syrian personnel. Russia, Iran, Syria and Lebanon have blamed the attack on Israel, which has declined to comment but has struck Syrian targets before.

Shamanov, who said local investigators found no trace of chemical weapons at the site of the reported attack, condemned Israel's unilateral airstrike. Russia has maintained a working relationship with Israel despite allying with Iran to help Assad overcome a 2011 uprising by insurgents and jihadis, including the Islamic State militant group (ISIS). It has also helped build up Syria's air defenses, which reportedly intercepted a number of missiles Monday and shot down an attacking Israeli jet in February. The Israeli incursion reportedly came in response to an Iranian drone crossing into Israeli airspace.

ABC News reported Tuesday that the Syrian military deployed missile defense systems near Assad's presidential palace in Damascus and that the U.S. destroyer was in striking distance of the country. Russian Beriev A-50 early-warning aircraft were deployed to the coast, according to Iran's semiofficial Fars News Agency. The elite Black Sea Fleet has declared a state of alert, according to Al Jazeera.

RTX5KUSF

INSTITUTE FOR THE STUDY OF WAR/REUTERS

Last month, Russia's top general, Valery Gerasimov, warned that his armed forces would "target both the missiles and their delivery vehicles" if a U.S. strike endangered the lives of Russian personnel, who were present at a number of Syrian military installations.

Most popular: Is the Devil Real? Pope Francis Says Fake News Comes From Hell, Which Does Exist

The U.S. and a number of allies initially supported the 2011 rebellion against Assad, but the Pentagon later focused on battling ISIS as the jihadis swallowed much of the Syrian opposition. As the militants lost territory nationwide in the years since, the multinational battle against them has taken a back seat to renewed tensions among local, regional and international forces, especially the U.S., Russia, Iran and Turkey. The Syrian government recognizes only Russia and Iran's military presence as legitimate.

Turkey, an ally of both the U.S. and Russia, launched a major incursion in January aimed at dislodging U.S.-backed Kurdish fighters, many of whom have since fled the U.S.-led battle against ISIS to take on the Turks and their Syrian rebel allies. The offensive has brought the Kurds closer to Assad and was followed by clashes between pro-Syrian government forces—including Russian citizens—and the mostly Arab remnants of the Syrian Democratic Forces in the east.

On Monday, Defense Secretary James Mattis said he "would not rule out anything" in terms of a U.S. military response in Syria. Last month, Mattis said that a sequel to the clashes between pro-Syrian government forces and the Syrian Democratic Forces was avoided when U.S. military leaders contacted their Russian counterparts via a de-confliction line.

RTX29U7Z

U.S. Navy/Reuters

Asked if the de-confliction lines were being used to currently inform Russian military officials of any potential U.S. action, the U.S.-led coalition said it was speaking to Russia specifically about strike operations within the al-Tanf area, a southeastern desert outpost. It has been the setting for violence between U.S.-backed and pro-Syrian government forces in the past, and Russia has accused the U.S. of using the site to shield remaining ISIS fighters, a charge the Pentagon has dismissed.

"The de-confliction lines for air and ground operations are professional discussions that have successfully ensured continuous communication, preventing accidental targeting or needless escalation in tensions between Russian-backed Syrian regime forces and Coalition-backed Syrian Democratic Forces and vetted opposition groups," the coalition told Newsweek in a statement.

As a potential crisis continued to develop, the White House said Trump would not attend the Summit of the Americas or make his debut Latin American tour and would instead "remain in the United States to oversee the American response to Syria and to monitor developments around the world." The statement said Vice President Mike Pence would go in his place.

This article was first written by Newsweek

More from Newsweek