Gunfire from the Syrian side of the border has hit a refugee camp inside Turkey, wounding at least three people.
Two Syrian refugees and one Turkish translator were wounded in Monday's incident when the Kilis border refugee camp in Gaziantep province came under fire from the Syrian side of the border, a Turkish foreign ministry official said.
However, it is unclear whether the camp was deliberately targeted.
A Turkish foreign ministry official said the Syrian charge d'affaires in Ankara was summoned to the ministry following the incident.
"We demanded an end to this (shooting)," the official said.
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Al Jazeera's Anita McNaught, reporting from Antakya in southern Turkey, said the incident signifies "a remarkable escalation in tensions on this already tense cross-border area".
The incident occurred as reports indicated that Syrian government forces were trying to prevent refugees from entering Turkey.
Thousands of Syrians are sheltering in eight refugee camps set up in Turkey's southern provinces of Hatay and Gaziantep, while others have crossed into Lebanon, Jordan and Iraq.
Against this backdrop, a UN-brokered ceasefire agreement that is due to come into force on Tuesday is looking shaky after Bashar al-Assad’s government raised new, last-minute demands that were rejected by the country’s armed opposition.
Under the deal, brokered by Kofi Annan, the UN-Arab League special envoy, the Syrian army is scheduled to withdraw from protest cities on Tuesday, with a complete end to fighting set for 48 hours later.
But Syria has since said it would only carry out its side of the bargain if the rebels first handed over written guarantees to stop fighting, a demand rejected by the leader of the largest armed opposition group, the Free Syria Army (FSA).
China has urged Syria to stick to its earlier pledge to stop fighting and start pulling back its troops, while also calling on the opposition to honour its commitments.
Colonel Riad al-Asaad said the FSA was committed to the peace plan but would give guarantees only to the international community and not the Syrian government.
"It is not a regime that is ruling the country. It's a criminal gang. So we will not give guarantees to it," Asaad told Al Jazeera just hours after the government issued its demand on Sunday.
Asaad said that if the Syrian government abided by Annan's six-point plan to end the violence, the FSA would hold its fire. He demanded that the government withdraw its forces to bases and remove checkpoints from the streets.
Last week, Assad accepted the ceasefire agreement, which also called for the government and opposition fighters to lay down their arms by 6am local time on Thursday.
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For his part, Annan urged Syria's government to fully implement its commitment to the ceasefire, and condemned "a surge in violence and atrocities" that is occurring there.
The truce is meant to pave the way for negotiations between the government and the opposition over Syria's political future.
However, activists say Syrian troops are continuing their assault on flashpoint regions.
Forces loyal to President Assad have also shelled an area in the province of Idlib near the border with Turkey, leaving dozens dead or injured, opposition activists said on Sunday.
Around 90 tanks and armoured vehicles, backed by helicopters, bombarded the al-Rouge Plain, southwest of Idlib city, the provincial capital, Reuters news agency reported quoting activists inside Syria and on the border with Turkey.
The activists further said fighters from the FSA were surrounded in al-Bashiriya, one of about 40 villages in the plain.
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The Syrian National Council, as the main opposition umbrella group is known, called on Sunday for UN intervention after monitoring groups said 86 of those killed on Saturday were civilians.
Towns north of Aleppo have endured days of clashes and bombardment, prompting 3,000 civilians to flee over the Turkish border on Friday alone, about 10 times the daily number before Assad accepted Annan's plan 10 days ago.
Recep Tayyip Erdogan, the Turkish prime minister, said on Saturday the number of refugees entering Turkey was rising.
"At the moment, we have 24,000 Syrians who have entered Turkey. Of course, this number is rising," Erdogan said before departing on a trip to China.
"In particular, Kofi Annan has to hold firm. He announced a deadline of April 10. I believe that he should monitor the situation very closely."
The UN estimates that at least 9,000 people have been killed in Syria since the crisis began 13 months ago.
Source: Al Jazeera and agencies