Opposition says new assaults may render peace efforts 'meaningless'.

Syrian troops backed by fighters from Lebanese militant group Hezbollah launched an assault on the rebel-held central town of Qusair on Sunday after months of fierce fighting in the area, observers said.

A man contemplates a damaged building in Homs, Syria, on Sunday.[Photo/Agencies]

The Syrian opposition condemned "attempts to invade" the town, which it said could render US-Russian attempts to organize a peace conference "meaningless".

State television said the army had "tightened the noose on the terrorists, attacking on different fronts and destroying positions of their leaders in the south of the town".

Meanwhile, Syrian activists say government airstrikes and heavy shelling of Qusair near the Lebanese border have killed at least 16 people, including rebel fighters.

The rebel-held town is home to about 20,000 residents and has been besieged for weeks by government troops. Opposition activists say members of the Lebanese militant Hezbollah group are also fighting with President Bashar al-Assad's troops in the area.

Qusair is strategically important because it links Damascus with the coast, where government forces are concentrated. This includes Alawites, followers of a Shiite offshoot to which the Assad family belongs.

The ground assault began after a heavy early morning bombardment of the town by aircraft and artillery, which killed at least 20 people, including 11 rebel fighters, activists said.

The Syrian Revolution General Commission, a network of activists on the ground, also reported the intense bombardment.

Key objective

"A rain of shells fell on the city at the same time as artillery fire and mortar fire from dawn. Homes were destroyed and burned down," the group said.

The Syrian government has made recapturing the town of Qusair and the surrounding Homs province a key objective. Fierce fighting has raged in the vicinity for months.

In recent weeks, government troops backed by Hezbollah and members of the National Defense Force, a pro-government militia, have advanced in the region, taking a string of villages and reportedly surrounding Qusair on three sides.

Last week, a military source said the army dropped leaflets on the town, warning civilians to leave ahead of an imminent military operation.

But activists denied the leaflets were dropped and said there was no safe way out of the city anyway.

Responding to news of the assault, the Syrian National Council, a key component of the opposition, denounced the "barbaric and destructive bombing" of Qusair.

It accused the government of working with Hezbollah to "invade the town and wipe it and its residents off the map".

"We say to the countries that are working for a political solution in Syria that allowing this invasion to go ahead in silence ... will render any conference and any peace effort meaningless," the group said in a statement.

The United States and Russia are working to organize a peace conference next month, in a bid to find a political solution to the conflict.