An international push to end Syria's conflict stalled Sunday as U.N. envoy Kofi Annan left Damascus without a cease-fire and President Bashar Assad's forces pounded opposition areas and clashed with rebels throughout the country.

Western and Arab powers are struggling for ways to stem the bloodshed in the year-old conflict while both the regime and the opposition reject dialogue. Former U.N. Secretary General Kofi Annan appeared to make little progress during two visits with Assad during his first trip to Syria as the joint U.N.-Arab League envoy.

Annan was seeking an immediate cease-fire to allow for humanitarian aid and the start of a dialogue between all parties on a political solution. After meeting with Assad on Sunday, Annan said he had presented steps to ease the crisis, but gave no details.

"Once it's agreed, it will help launch the process and help end the crisis on the ground," he told reporters. He called for "reforms that will create a strong foundation for a democratic Syria -- a peaceful, stable, pluralistic and prosperous society, based on the rule of law and respect for human rights."

But he said a cease-fire must come first.

"You have to start by stopping the killing and the misery and the abuse that is going on today and then give time for a political settlement."

Assad told Annan on Sunday that a political solution is impossible as long as "terrorist groups" threaten the country, according to Syria's state news service -- which reported identical comments after the men met Saturday. The regime blames the uprising on armed groups acting out a foreign conspiracy.

Annan's calls for reform also fall far short of opposition calls for Assad's ouster and the end of his authoritarian regime. Opposition leaders say the thousands killed at the hands of his security forces, many while protesting peacefully, mean they'll accept nothing less.

Annan acknowledged his hard task.

"It's going to be difficult, but we have to have hope," he said before leaving for Qatar.

The conflict has become increasingly bloody during the year since protesters in some impoverished provinces first took to the streets to call for political reform. The government has cracked down hard, and protests have spread, with some in the opposition taking up arms to attack government troops and defend their towns and neighborhoods.

The U.N. says more than 7,500 people have been killed. Assad's regime and military have remained largely intact while the opposition, though disorganized, shows no sign of relenting on its demands. Few expect a swift resolution.

Government troops shelled areas in and around the northern city of Idlib, activists said, part of a campaign launched Saturday to crush the opposition in its stronghold along the border with Turkey. In some areas they clashed with local rebels fighting under the banner of the loose-knit Free Syrian Army.

The British-based Syrian Observatory for Human Rights, which relies on a network of activists around Syria, said 16 civilians had been killed in attacks by Syrian forces or in clashes with local rebels in Idlib province. More than five government soldiers were also killed.

An AP photographer in Turkish border villages heard constant artillery pounding, and Turkish residents said they saw Syrian refugees crossing during lulls.

The renewed violence has sent about 1,000 Syrians across the border in the past week, as many as fled during the previous month, a Turkish official said. He spoke on condition of anonymity under government protocol.

Turkey now hosts about 12,500 Syrians, some of the more than 100,000 refugees who have fled to Turkey, Lebanon and Jordan.

Many fear the offensive in Idlib could end up like the regime's campaign against the rebel-held neighborhood of Baba Amr in the central city of Homs. Troops besieged and shelled Baba Amr for almost a month before capturing it on March 1.

Activists say hundreds were killed, and a U.N. official who visited the area last week said she was "horrified" by the destruction in the nearly deserted district.

Activists said Syrian forces targeted other Homs neighborhoods on Sunday with shells and rocket-propelled grenades.

"There is very heavy destruction. Cars are burning and smoke is rising from the area," said an activist from Homs who goes by the name Abu Bakr Saleh. "They are trying to punish all districts of Homs where anti-government protests still take place."

Other activists said government forces shelled a bridge on a road to the Lebanese border often used by families fleeing violence. It was unclear whether the bridge was destroyed.

The Observatory said 25 civilians had been killed in military attacks and clashes between army and rebel forces across Syria on Sunday. Another group, the Local Coordination Committee's said 32 were killed.

The death tolls could not be independently verified. The Syrian government rarely comments on specific incidents and bars most media from operating inside the country.

Also Sunday, gunmen in the northwestern city of Aleppo killed local boxing champion Gheyath Tayfour. Syria's state news agency said an armed group ambushed the 43-year-old boxer in his car near Aleppo University and shot him dead.

Tayfour was not known to have voiced opinions on the country's conflict, making it unclear whether his killing was politically motivated.

Syria has seen a string of mysterious assassinations lately targeting doctors, professors and businessman as the uprising has grown more militarized.