European Union (EU) foreign ministers have decided to impose more sanctions on Syria as violence persists in the Arab country despite a UN-backed peace plan.

In the 15th round of EU sanctions against Syria, the ministers on Monday agreed on an assets freeze and visa ban on two firms and three people that financially supported its government.

So far, a total of 128 persons and 43 firms in Syria are on the EU sanctions list.

"The EU sanctions target the Syrian regime, not the civilian population. As long as the repression continues, we will continue to put pressure on those responsible for it," EU foreign policy chief Catherine Ashton said.

"We will continue to support him (Kofi Annan) for as long as he wishes to continue with this mission ... because the six-point plan will make a significant difference and real progress towards the change we think needs to happen," she said.

Contrary to the EU, Russia believed that the opposition, not the Syrian government, is responsible for the ongoing violence in Syria.

Russian Deputy Foreign Minister Gennady Gatilov said Monday that Moscow considered it wrong to leave the Syrian government unarmed while the opposition receives weapons, and that Russia would continue its military technological cooperation with Syria.

"Everything which is shipped to Syria (from Russia) has been done on the legal ground. We do not dispatch offensive arms there, only defensive ones," he said.

The official also warned that Russia would oppose any UN resolution that authorizes military intervention in Syria.

Though the UN-backed six-point plan has been in effect since April 12, it has contributed little to restore calm in the unrest-torn country.

On Monday, two army officers were killed by armed groups in Damascus and the southern province of Daraa, raising the death toll of senior army officers over the past months to at least 16.

After the two incidents, another six troops, including an officer, were killed when an armed group attacked a Syrian border guards' post in a suburb of Damascus.

Also on Monday, the UN Supervision Mission in Syria (UNSMIS) confirmed that one of its vehicles was hit by a bullet on Sunday near the city of Homs.

"No peacekeepers were injured, and there was no significant damage," UN spokesman Martin Nesirky said at a daily news briefing. "It is unclear who fired on the peacekeepers."

This was the third attack targeting the UN observers since their arrival.

With a total mandated strength of 300 unarmed military observers and additional civilian staff as required, the UN mission continues to receive new members on a daily basis as it expands its presence across the Middle East country.

Six Chinese working as UN military observers arrived there on Monday to join the 189-member team already on the ground upon the world body's request.

In the Arab world, Saudi Arabia expressed less confidence in the peace plan, while Jordan and Egypt urged a political solution to address the crisis in Syria.

"The violence is still continuing, the bloodshed is still continuing. Nothing has been accomplished except the violence has lessened. The violence continues ... nobody is satisfied," Saudi Foreign Minister Prince Saud al-Faisal said at a news conference in Riyadh after a meeting of Gulf Arab leaders.

"Confidence in the efforts of the envoy of the United Nations and the Arab League has started to decrease quickly," he said.

Meanwhile, Jordanian Foreign Minister Nasser Judeh and his Egyptian counterpart Mohamed Kamel Amr at a meeting underscored the need for protecting the Syrians and putting an end to the year-long Syrian crisis.

The Arab League (AL) said Monday that the meeting of Syrian opposition groups previously scheduled to be held on Wednesday was postponed upon the request of the Syrian National Council and the Syrian National Coordination Body for Democratic Change.

At a special ministerial meeting on April 26, the AL decided to invite all Syrian opposition groups to meet in Cairo.