Warplanes strike Syrian town where chemical attack killed dozens, activists say One woman was killed and another person was injured in Saturday's airstrike.

 -- Warplanes bombarded a town in northern Syria on Saturday where a chemical weapons attack killed scores of people earlier this week, according to Syrian opposition activists.

The Syrian Observatory for Human Rights, a Britain-based monitoring group, said Saturday’s airstrike on the eastern side of Khan Sheikhoun in Idlib province killed a woman and wounded another person. It’s the first death in the town since Tuesday’s chemical weapons attack that killed at least 87 civilians, including 31 children.

Saturday’s airstrike was accompanied by heavy machine guns, according to the Syrian Observatory for Human Rights.

The nationality of the warplanes is unknown.

The United States is leading a coalition of countries that conducts airstrikes targeting ISIS in Syria. There are also 900 U.S. troops on the ground advising and assisting the U.S.-backed Syrian Democratic Forces (SDF) fighting ISIS.

Meanwhile, Russia, which launched its military operation in support of Syrian government forces in September 2015, has an estimated 4,000 troops in Syria and is Assad’s key backer.

What started as a local protest movement in Syria’s southern city of Dara'a expanded into a full-fledged civil war by 2012. ISIS, which grew out of al-Qaeda in Iraq, took root in northern and eastern Syria in 2013 after seizing swaths of territory in neighboring Iraq. The jihadist group is fighting to overthrow Assad's regime and establish a caliphate.

The Syrian Civil War has pulled in the United States, Russia, Iran and almost all of Syria's neighbors. It has become the largest humanitarian crisis since World War II, according to the United Nations.

Tuesday’s chemical attack is the latest atrocity in Syria’s six-year conflict.

Harrowing footage from the scene shows victims gasping for air and being hosed off, as well as the lifeless faces of those who didn’t survive. It's the worst chemical attack the war-torn country has witnessed since 2013.

The United States has blamed Syrian President Bashar al-Assad’s regime for the attack and responded by launching airstrikes against a Syrian government air base on Thursday night.

Syria's government has firmly denied carrying out the chemical attack and has lambasted the United States for bombing its Shayrat Air Base in Homs province, which the Syrian Observatory for Human Rights said killed eight people and wounded others.

Russia, which has continued to stand by Assad’s regime, has said that toxic agents were released when a Syrian airstrike hit a warehouse where opposition militants were storing chemical weapons -- a statement that contradicts testimony from residents, doctors and activists on the ground.

Two Syrian jets took off from the air base -- one day after it was hit by U.S. missiles – and conducted airstrikes on ISIS-held areas in the countryside of eastern Homs, according to the Syrian Observatory for Human Rights.

ABC News' Benjamin Gittleson, Alexander Mallin, Luis Martinez, Alexander Marquardt, Lena Masri, Kirit Radia, Patrick Reevell, Joseph Simonetti, Daniel Trefcer and Marcus Wilford contributed to this report