Hama, Syria - Syrian rebel forces captured the central city of Hama on Thursday, overrunning forces loyal to President Bashar al-Assad only days after taking over Aleppo in a lightning offensive.

The rebels led by the Salafist group Hayat Tahrir al-Sham (HTS) stormed the city and, after fierce fighting, claimed to have seized its prison and released inmates.

After a night of violent clashes, the rebels entered Hama "from several sides" and were engaged in street fighting with Assad's forces, said the Syrian Observatory for Human Rights war monitor.

By early Thursday afternoon, Syria's army admitted it had lost control of the strategically located city seen as crucial in its efforts to protect the capital and seat of power, Damascus.

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"Over the past few hours, with the intensification of confrontations between our soldiers and terrorist groups... these groups were able to breach a number of axes in the city and entered it," the army said, adding units had redeployed outside the city.

The fall of Hama came despite shelling and strikes carried out by the Syrian and Russian air forces, as reported by state media late Wednesday.

The Syrian Observatory for Human Rights, which relies on a network of sources in Syria, says 727 people, mostly combatants but also 111 civilians, have been killed in Syria since the violence erupted last week.

It marks the most intense fighting since 2020 in a country already ravaged by civil war, which erupted with the repression of pro-democracy protests in 2011.

Key to the rebels' successes since the start of the offensive last week was the takeover of Aleppo, which in more than a decade of war had never entirely fallen out of government hands.

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The head of HTS, Abu Mohammad al-Jolani, on Wednesday visited Aleppo's landmark citadel.

Jolani was seen waving to supporters from an open-top car as he visited the historic fortress, in images posted on the rebels' Telegram channel.

While the advancing rebels found little resistance earlier in their offensive, the fighting around Hama has been especially fierce.

Assad ordered a 50% raise in career soldiers' pay, state news agency SANA reported, as he seeks to bolster his forces for the counteroffensive.

Syrian armed forces were driven back by the rebels despite the government sending in "large military convoys," according to the Observatory.

The monitor said the fighting on Wednesday was close to an area mainly populated by Alawites, followers of the same offshoot of Shiite Islam as the president.

The rebels launched their offensive in northern Syria on November 27, the same day a ceasefire took effect in the war between Israel and Hezbollah in neighboring Lebanon.

Both Hezbollah and Russia have been key backers of Assad's government, but have been more recently mired in their own respective conflicts, with Israel and Ukraine respectively.

The US also has a military presence on the ground and has conducted airstrikes over the past year against groups supported by Iran, as well as what remains of ISIS.

The UN on Wednesday said 115,000 people had been "newly displaced across Idlib and northern Aleppo" by the fighting.

Human Rights Watch warned the fighting "raises concerns that civilians face a real risk of serious abuses at the hands of opposition armed groups and the Syrian government."