Speaker Paul Ryan Paul Davis RyanKenosha will be a good bellwether in 2020 At indoor rally, Pence says election runs through Wisconsin Juan Williams: Breaking down the debates MORE (R-Wis.) in a tweet on Sunday condemned reports of a deadly chemical attack on civilians in Syria, saying responsible countries cannot tolerate it.

"The chemical attack in Syria is a horror that cannot be tolerated by responsible nations," Ryan tweeted.

"The U.S. must continue to lead an international effort to hold the Assad regime and Russia accountable for their actions," he added, referring to Syrian President Bashar Assad.

The chemical attack in Syria is a horror that cannot be tolerated by responsible nations. The U.S. must continue to lead an international effort to hold the Assad regime and Russia accountable for their actions. — Paul Ryan (@SpeakerRyan) April 8, 2018

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Ryan's comments followed a Saturday attack on the rebel-held town of Douma that reportedly left dozens of Syrian civilians dead and hundreds others injured.

The Trump administration has lashed out at Assad's government, which has denied any role in the attack, as well as Russia and Iran.

President Trump Donald John TrumpBubba Wallace to be driver of Michael Jordan, Denny Hamlin NASCAR team Graham: GOP will confirm Trump's Supreme Court nominee before the election Southwest Airlines, unions call for six-month extension of government aid MORE early Sunday called out Moscow and Tehran for supporting Assad.

Many dead, including women and children, in mindless CHEMICAL attack in Syria. Area of atrocity is in lockdown and encircled by Syrian Army, making it completely inaccessible to outside world. President Putin, Russia and Iran are responsible for backing Animal Assad. Big price... — Donald J. Trump (@realDonaldTrump) April 8, 2018

The State Department also called for the Kremlin to end its support for Assad.

State Department spokeswoman Heather Nauert said in a statement that Russia “ultimately bears responsibility for these brutal attacks.”