BUKULMEZ, Turkey, April 6 (Reuters) - Syrian forces are pressing a military offensive and laying mines near the border with Turkey in an attempt to block a flow of refugees and supplies for insurgents, rebel activists and a Turkish official at the frontier said on Friday.
Syrian army activity, visible across olive groves from the small Turkish border village of Bukulmez, comes days before a ceasefire deadline agreed by President Bashar al-Assad. The flow of refugees to Turkish camps nearby swelled to 2,800 on Thursday as violence in the bordering Idlib province worsened.
"The whole of northern Idlib has become another Baba Amr," said Ahmed Sheikh, a law student and activist, referring to a district of the town of Homs devastated by shelling in the past two months.
It was impossible to verify reports from the many refugees fleeing Syria since foreign correspondents' access to the country is strictly limited by the Damascus government.
A Syrian helicopter could be seen hovering over mountains on the Syrian side of the border in clear view of refugees at a camp. A Reuters television journalist with experience in the area said it was the first time since the crisis began that he was aware of Syrian aircraft flying close to Turkey.
Villagers reported hearing artillery along the border.
A Turkish foreign ministry official touring the camps in the area said there was new activity close to the border.
"The Syrians have been mining the border, especially the southern Idlib part which has been restricting the flow of refugees," the official said. He declined to give his name.
Activists said mining was concentrated on southerly parts of Turkey's border with Syria, from the town of Harem westwards to the coast.
"Assad is using the days granted to him by the international community to choke off the refugee movement to Turkey and the delivery of any kind of aid," said Muhammad Abdallah, a rights campaigner from Idlib.
He said most of the border area from the Mediterranean coast was closed, leaving only a 10 km (six mile) corridor along a valley near Rehanyi which the rebel Free Syrian Army controls.
"But I dont expect this to last for long because we have seen nearby villages and towns come under intense helicoper, tank and artillery bombardment," he said.
Still, refugees were getting through, the flow rising to 2,800 on Thursday.
In Ankara, Turkish Foreign Minister Ahmet Davutoglu demanded Assad keep his promise to cease military operations.
"At the moment the number of refugees to have entered Turkey is 23,835. If more refugees come then the United Nations and international community must take action," he told reporters.
Under an internationally backed plan agreed with Damascus, government forces should cease operations and withdraw from settlements by April 10. Rebels should then cease fire within 48 hours.
U.N. special envoy Kofi Annan said on Thursday he had been told by Damascus that troop withdrawals were underway from Idlib, as well as Zabadani and Deraa. But U.N. Secretary General Ban Ki-moon said on Friday the conflict was worsening and attacks on civilian areas persisted.
The flow of refugees has been a big concern for Turkey which long saw Damascus as a regional friend but is now in the forefront of diplomatic opposition to Assad and gives refuge to civilian and military forces ranged against him.
Turkey fears that a complete breakdown in Syria would unleash a flood of refugees reminiscent of the half million who descended on Turkish territory from Iraq during the Gulf War in the early 1990s.
Ankara officials have cited such a development as one of the few that might make it consider establishment of a safe zone on the Syrian side. The presence now of Syrian troops so close to the border would make such a move perilous.
Abdallah said government forces were trying as far as possible to cut off refugees well before the border. The two main highways into Turkey from Aleppo and the provincial capital of Idlib had been cut off by army roadblocks.
A member of the FSA who goes under the nom de guerre of Abu Seif said that for government forces "the name of the game is control".
"The tactic being used to stop the flow of refugees is heavy bombardment of strategic villages or towns on the border with Turkey. Then they mine around these towns and villages."
An opposition activist said the refugee flow into Turkey varied greatly from day to day because government troops would find open areas and shut them down. Refugees would then probe for new crossings and then pour across until they were blocked.
One particularly dangerous crossing is the Orontes River, which marks the border and is famous for its strong currents. Syrian army tents could be seen pitched amid lush farmland on the other side.
Syrian opposition activists said four refugees were shot dead trying to cross the river this week and a 16-year-old boy drowned. The activists said the Syrian army fired at and sank barrels used as makeshift boats pulled by ropes.
"Behind the tents there are army machinegun positions. If Assad lets the people escape you would see hundreds of thousands of Syrians here," said Mohammad Hijazi, who was elected as a representative of refugees in Boynuyogun camp, one of several camps Turkish authorities set up right on the border.
"Every time the regime is given a deadline it is a catastrophe. Assad interprets it as a licence for unlimited killing and another deadline is set," Hijazi said.