United Nations: With the deadline for the Syrian government to halt use of heavy weapons and withdraw troops from population centres closing in, UN-Arab League joint envoy Kofi Annan said efforts have to be intensified to end the bloodshed or else Syria could "plunge into an abyss."

Annan urged the Bashar-Al Assad-led Syrian government and opposition forces to stop the violence, stressing that all hostilities must end by Thursday morning.

"There is no more time to lose. We must all push for an end to the bloodshed before Syria plunges into the abyss," Annan said in a statement issued here.

Last week, the Syrian Government had told Annan that it would cease use of heavy weapons and complete the withdrawal of troops from population centres by April 10.

The former UN chief had said once the government forces fulfill their commitment, all parties, including the opposition, should move immediately to cease all forms of violence so that a complete cessation is in place by 0600 hours Damascus time on April 12.

However, Syrian forces opened fire across the Turkish border that resulted in deaths and injuries, reports said.

UN Chief Ban Ki-moon said he is "alarmed" by the reports of ongoing violence and human rights violations in Syria.

A UN team is in the country to start technical preparations for the potential deployment of observers to monitor a cessation of armed violence and the full implementation of Annan’s six-point peace plan.

Annan expressed optimism that there is still hope for his peace plan, which was submitted last month during his visit to Damascus, to be implemented.

"We still have time between now and the 12th to stop the violence and I appeal to all concerned, the Government in the first place, and the opposition forces," Annan said.

"I believe it's a bit too early to say that the plan has failed," Annan said.

"The plan is still on the table and it's a plan we are all fighting to implement. It's a plan the Council has endorsed, a plan the Syrians have endorsed, and from the comments made by the opposition they are also prepared to go along with it if the Government meets its commitments to pull the troops out. So the plan is very much alive."

Annan said he would submit a report to the UN Security Council today sharing the information he has received from the Syrian government on troop withdrawals, and stated that there have been indications of the government withdrawing in various cities.

However, he expressed concern over reports from other sources indicating that there have been military movements to other areas which have not previously been targeted.

"We are not on the ground yet. One of the things that we are discussing is a UN monitoring mission that will monitor and supervise the cessation of violence," Annan said, underlining that a presence in the country will help to monitor, observe and report on the situation.

Meanwhile, the UN High Commissioner for Refugees (UNHCR) is sending a team to provide technical assistance to nine camps in the border between Turkey and Syria, which have so far been run by Turkish authorities.

UNHCR spokesperson Adrian Edwards told a news briefing in Geneva that a plane with 1,600 tents and 1,400 blankets was sent to Turkey on Wednesday, and stressed that the agency is working closely with the Turkish authorities to ensure the supplies are distributed locally.

Currently, there are 24,564 registered Syrian refugees in Turkey; 10,112 in Lebanon; 7,021 in Jordan; and 792 in Iraq.

Annan said as a "tragic consequence" of the Syrian crisis, nearly 25,000 people - 6,000 of them in the last five days alone have fled the fighting across the border into to Turkey.

"Their stories were heart-wrenching... We must work to create the conditions for them to return to their homes sooner rather than later," he said.