Greek authorities said Turkish guards along the northern border by the Evros River again fired shots into the air in a further provocation continuing to ramp up tension amid worries Turkey would now try to send more refugees and migrants to overwhelmed Greek islands.

The new incidents happened in a 24-hour period, the first the night of May 5 when Hellenic Police and Army officers reported hearing shots coming from near the village of Marasia, which is on the riverbank, said Kathimerini.

The next afternoon, more shots were fired by Turkish police who were on patrol along the river near the Greek village of Tychero, Greek officials said, repeating a similar event on April 30 when Turkish military border officers fired shots into the air near Tychero, which is also right on the borderline.

Greek security officials were said to believe this is a deliberate campaign to keep pressure on Greece while some reportedly said Turkey is trying to control crossing points by the river where hundreds of refugees and migrants over the previous four years have crossed, many drowning in the perilous currents.

The border is where Turkish President Recep Tayyip Erdogan in February had 10,000 migrants sent in a bid to get them across into Greece after the deaths of 33 Turkish soldiers in an area of northern Syria they had invaded.

He said that made him worry that Turkey, which is holding 3.3 million Syrian refugees from that country’s civil war, and 2.2 million from other countries, would be inundated and he wanted to relieve the pressure.

Under an essentially-suspended 2016 swap deal with the European Union, which closed its borders to refugees and migrants, Turkey is supposed to contain them in return for 6 billion euros ($6.47 billion,) – only half of which has been given – while other pledges from Europe haven’t been met so far.

The migrants sent to the land border were pulled back at the end of February after Greece closed its side and sent riot police and Army units to stymie them but tensions remained in the region.