BEIRUT, Lebanon — Syrian forces bombarded the city of Homs for a sixth day in a row on Friday, while government soldiers backed by Hezbollah fighters clashed with rebels on the outskirts of the city’s besieged Khalidiya neighborhood amid warnings from international health officials that fighting was increasingly preventing humanitarian aid from reaching those most in need.

Government forces have trained their sights on Homs and the northern city of Aleppo in recent weeks since they recaptured the strategic border town of Qusayr last month. Antigovernment activists have said the government was aided in the battles by fighters from Hezbollah, the Lebanese Shiite militant group.

The group has not confirmed that, saying only that it would go where it was needed to fight off the insurgency against Syria’s president, Bashar al-Assad, which Hezbollah leaders say threatens Lebanon and the region.

On Friday, clashes intensified near the Khalidiya district, which the army has been trying to storm for weeks, according to the Syrian Observatory for Human Rights, a Britain-based watchdog group with a network of activists in Syria.