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SANA, Associated Press
In this photo released by the Syrian official news agency SANA, Syrian President Bashar Assad, center, attends the Eid al-Fitr prayer marking the end of the Muslim fasting month of Ramadan at the Khair mosque, in Damascus, Syria, Monday, July 28, 2014.

BEIRUT — Syrian President Bashar Assad prayed at a Damascus mosque at the start of a major Muslim holiday on Monday amid reports of an unprecedented high death toll among his troops battling Islamic extremists.

The military casualties came as fighting intensified in the past two weeks, with militants from the al-Qaida-breakaway Islamic State group seeking to eliminate opponents from all sides, dealing a series of setbacks for government forces and rival rebels alike.

The Britain-based Syrian Observatory for Human Rights said about 1,240 soldiers and other Assad loyalists have been killed in the past 10 days in northern Syria.

They are among more than 1,800 people killed in the same period — a record number of deaths since the uprising against Assad began in March 2011, according to Rami Abdurrahman, the Observatory's director.

Other activists in Syria confirmed that past weeks have seen a record death toll. Syria's three-year civil war has already killed more than 170,000 people, nearly a third of them civilians, according to activists.

However, the Syrian government has not reported on the heavy losses. State TV on Monday showed Assad performing prayers in Damascus' Khair mosque earlier in the day, smiling as he greeted Muslim clergymen. It was his second public appearance in less than two weeks.

Despite the raging civil war, Assad was re-elected last month in a vote that was confined to government-controlled areas and dismissed by the opposition and its Western-allies as a sham.

He was sworn in for a third seven-year term a lavish ceremony on July 16. In his inauguration speech, he confidently declared victory and praised his supporters for "defeating the dirty war" against Syria.

The government losses began shortly after that speech, as fighters from the Islamic State group launched attacks against army positions in northern and central Syria. In the past week alone, the militants captured a government-controlled gas field and two major army bases in three different provinces.

Beyond Syria, the Islamic State fighters have also seized large swaths of land in northern and western Iraq in a blitz offensive that began last month, and have declared a self-styled caliphate across the territory they now control, straddling the Iraq-Syria border.

They have since been fighting to expand their area of control.