"The toll of today's martyrs reached 32, and 50 others were wounded," the operations room set up by the new Government of National Unity (GNA) said on its Facebook page and Twitter account late Wednesday, updating an earlier toll of 18 dead.
Of the earlier toll, seven died in a car bomb attack in Buairat el-Hassun, 60 kilometres (35 miles) west of Sirte and the others were killed in an IS foray in Abu Grein, further west, that the GNA recaptured on Tuesday.
The GNA on Tuesday called for warplanes to bomb IS after world powers showed readiness to arm it.
On Monday, the United States, Italy and Libya's allies and neighbours agreed in Vienna to arm the GNA to confront the threat from IS.
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Clashes on Tuesday claimed the lives of seven members of the GNA forces and wounded 15.
IS overran Abu Grein on May 5 as part of a series of forays into territory controlled by the UN-backed government, including a deadly attack a week later on a checkpoint at Saddada, 50 kilometres to the west.
The latest fighting comes as IS seeks to expand westwards out of Sirte, slain dictator Moamer Kadhafi's hometown on the Mediterranean coast, which it has controlled since last June.
Europe fears the jihadists could use Sirte's port and airport as a springboard to attack the continent.
The international community, particularly European powers, are also concerned about a stream of refugees and migrants crossing the Mediterranean from Libya's unsecured coast.