Greek officials are nervous that Bulgaria's entry into the visa-free Schengen Agreement could see activity return to its border with Turkey, according to Euobserver.

"We faced a huge problem, a humanitarian crisis. That's why we asked for the help of Frontex," Brigadier General Georgios Salamagkas, head of the police directorate of Orestiada - the small Greek town beside the country's short stretch of land border with its large eastern neighbour told Euobserver.

Salamagkas has witnessed the dramatic upsurge in border crossings in 2010, which was stemmed with the help of an EU support mission operating on Greece's border with Turkey.

In 2010, roughly 47,000 irregular immigrants – 90 percent of the EU total that year - were arrested after crossing the 200 kilometre Greek border with Turkey, a frontier for the most part demarcated by the River Evros.

Attracted to Turkey by a plethora of visa-free agreements signed between Turkey and several north African and Middle East states, over half that number opted to cross at the 12.5 kilometre land border with Greece close to Orestiada, the location for the planned building of a controversial fence.

"The border crossing there is very easy, they took advantage of it. The fence is one of the measures which can help," said Salamagkas.

But numbers have already dropped from over 7,600 last October to around 1,600 in February of this year, largely thanks to Frontex's Rabit operation which saw some 175 police officers from EU member states join the front line between November 2010 to March 2011. Another Frontex operation - Poseidon Land 2011 - will run on the Greek-Turkish border until the end of this year.

As well as the Frontex missions, the series of recent revolutions in northern Africa and renewed migratory flows to Italy's southern island of Lampedusa have further served to reduce pressure on Greece's eastern border, Euobserver comments.

Officials fear activity could shortly return to the area, however. North of Orestiada, Bulgaria shares a 209 kilometre land border with Turkey, with Sofia pressing hard to join the visa-free Schengen Agreement later this year. Membership is expected to increase the attractiveness of Bulgaria as an entry point into the EU.