Activists say Islamic State group seizes territory on edge of Syria's historic city of Palmyra

The White House and trees are reflected in a puddle on the White House complex, Saturday, May 16, 2015, in Washington. The Pentagon says U.S. commandos have mounted a rare raid in eastern Syria, killing the Islamic State commander in charge of oil fields in a firefight and capturing his wife. (AP Photo/Jacquelyn Martin) (The Associated Press)

The sun rises over the White House in Washington, Saturday, May 16, 2015. The Pentagon says U.S. commandos have mounted a rare raid in eastern Syria, killing the Islamic State commander in charge of oil fields in a firefight and capturing his wife. Defense Secretary Ash Carter announced the raid Saturday, identifying the militant as Abu Sayyaf. He said no U.S. forces were killed or injured. (AP Photo/Jacquelyn Martin) (The Associated Press)

FILE - In this Monday, Oct. 27, 2014 photo, a Syrian flag flies over the capital, Damascus, Syria. U.S. commandos mounted a rare raid into eastern Syria overnight, killing a senior Islamic State commander in a firefight, capturing his wife and rescuing a Yazidi woman held as a slave, the Pentagon said Saturday, May 16, 2015. Defense Secretary Ash Carter announced the raid, identifying the militant as Abu Sayyaf. He said no U.S. forces were killed or injured in the operation. (AP Photo/Diaa Hadid) (The Associated Press)

Activists say Islamic State militants are advancing toward the historic city of Palmyra in central Syria, seizing an oil field and taking control of the water company on the outskirts.

The advances in the Palmyra countryside were coupled with an announcement Saturday by the Islamic State group that its fighters have seized full control of Saker Island in the Euphrates River north of Deir el-Zour, the northeastern province divided between areas held by the group and the government.

The new gain, confirmed by the Britain-based Syria Observatory for Human Rights, leaves the Deir el-Zour military air base in the clear path of Islamic State fighters. It follows days of intense clashes.

Government forces and Islamic State fighters began battling on the eastern edge of Palmyra on Thursday.