U.N. Secretary-General Ban Ki-moon condemned a bomb blast Wednesday near a convoy of U.N. observers that was entering the southern Syrian city of Daraa.

"This attack is unacceptable," Ban told reporters at the United Nations. "Today's incident is an example of what the Syrian people have endured for the past 15 months. It is a testament to the difficulty and the danger of the task entrusted to our U.N. observers and it is a blunt reminder of the risks of violence escalating even further.

"There is no escaping the reality that we see every day: innocent civilians dying, government troops and heavy armor in city streets, growing numbers of arrests and allegations of brutal torture, an alarming surge in the use of IEDs and other explosive devices."

The bomb exploded near the convoy carrying U.N. observers and the head of the monitoring team in southern Syria. There were no casualties among the observers, but the Syrian government said 10 Syrian soldiers were wounded, according to a statement released on behalf of Ban. The observers were heading from Damascus to Daraa under Syrian army escort.

Ban called on government forces "and all elements of the opposition" to stop the violence. "If this opportunity is not seized, I fear that what joint special envoy Kofi Annan has warned about will come to pass: a full-scale civil war with catastrophic effects within Syria and across the region."

Annan is working on behalf of the United Nations and the Arab League to end the fighting.

Ban said it is imperative for the international community to support Annan's efforts.

"This was a graphic example of what the Syrian people are suffering on a daily basis and underlines the imperative for all forms of violence to stop," Maj. Gen. Robert Mood, head of the U.N. Supervision Mission in Syria and chief military observer, said in a written statement.

A "recent increase" in bombings and persistent violence "call into question the commitment of the parties to the cessation of violence and may have a direct impact on the future of the mission," the statement said.

The purpose of the observer mission is to monitor the status of the cease-fire and Annan's six-point peace plan.

Pro-government news agency Addounia TV, which had a crew in the convoy, said the blast damaged cars and a state-run Syrian TV photographer was "lightly injured."

"The explosion directly targeted the guards," Addounia TV said.

Sham News, a network of opposition activists who post information and videos on the Internet, said the blast occurred in the Manshiya neighborhood of Daraa when a military Jeep stormed the city and fired shots resulting in injuries. It said opposition Free Syrian Army forces "targeted the car and exploded" the vehicle.

"We deny that any of the people in the car were members of the international mission," Sham News said.

CNN cannot independently verify reports of violence and deaths within Syria as the government has restricted access by most of the international media.

Despite months of international sanctions, diplomacy and pressure on President Bashar al-Assad's regime, world leaders say an end to the bloodshed may still be far away.

Annan plans to return soon to Damascus to seek adherence to the cease-fire, which was supposed to go into effect April 12. He reiterated that the killing must stop immediately.

"There has been some decrease in the military activities, but there are still serious violations in the cessation of violence that was agreed," Annan told reporters after briefing the U.N. Security Council.

The Local Coordination Committees of Syria, an opposition network, said Wednesday that 1,025 Syrians have been killed since Annan's initiative. The dead include 42 women, 60 children (40 boys, 20 girls), 22 people who died under torture.

The U.N. observer mission comprises 113 personnel from 38 countries, including 70 military observers and 43 civilian staff members and is mandated to have 300 military observers and about 100 additional civilian staffers. It has been operating in Damascus, Homs, Hama, Idlib, Aleppo and Daraa. It is regularly receiving new members and expanding.

"In the next two days, we will cross the 100 mark for military observers in the mission," Mood said.

At least 20 people were killed Wednesday in Syria, the LCC said. The deaths occurred in Homs, Hama, Idlib, Deir Ezzor, Aleppo and the Damascus suburbs.

Susan Rice, the U.S. ambassador to the United Nations, said the United States maintains its position that al-Assad has lost all legitimacy and must step down. If the violence persists, she said, the Obama administration is ready to look at other means to ratchet up pressure on Damascus, including a renewed discussion in the Security Council.

On Monday, Ban said the Syrian situation has become one of the "most serious and gravest concerns of the international community."

"More than 9,000 people have been killed during the last 14 months. This is totally unacceptable and an intolerable situation," Ban said.