ELBEYLI, Turkey (Reuters) - Slabs of concrete wall have sprung up and military patrols have intensified, but local people say this stretch of Turkey’s border facing Syrian territory under Islamic State control is still far from water-tight.

A Kurdish People's Protection Units (YPG) fighter walks near a wall, which activists said was put up by Turkish authorities, on the Syria-Turkish border in the western countryside of Ras al-Ain, Syria January 29, 2016. REUTERS/Rodi Said

Ankara is under intense pressure from its NATO allies to seal off the 70 km (40 mile) strip that stretches from just east of the Turkish town of Kilis to Karkamis, long a conduit for fighters, smuggled goods and war materiel.

Beyond a string of tiny villages nestled in undulating fig and olive groves lies the last stretch of Syrian territory on Turkey’s southern frontier that Islamic State militants still hold, following advances by rival Kurdish rebels.

European governments fear that their own citizens who have fought with the jihadists could still cross back into Turkey before heading home to stage attacks.

Likewise, the United States believes Turkey, which has NATO’s second largest army, must close the frontier if Islamic State is to be defeated in Syria.

Soldiers patrol in armored vehicles along a border delineated in some places by little more than razor-wire fence. Additional watchtowers and huts have appeared in recent months, and three-meter (10 foot)-high concrete slabs are being erected along some of the most vulnerable sections.

But the efforts by a nation which had long been criticized for failing to do more to prevent the passage of foreign fighters appear to have come too late to stop Islamic State networks developing inside Turkey.

Washington and Ankara have been discussing for months how to seal this stretch of border. Senior U.S. officials said last month they would offer Turkey technology including surveillance balloons and anti-tunneling equipment.

Border security is now undoubtedly tighter but, for those wanting to sneak over, not absolute - and help remains available for a price.

“It’s difficult, but not impossible,” said Ismail, a 37-year old who described himself as a trader, smoking a cigarette in a tea house near the village of Akinci.

“Let’s say you want to cross. You tell me where and when and I can call people who will make it happen,” he said. “But you would have to pay more.”

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The military’s own figures suggest attempts to cross into Islamic State-held Syrian territory have continued, showing 121 people tried over the past 10 days alone. Almost half were children, and at least a dozen were foreigners.

Nevertheless, it is cracking down on those trying to spirit people over the border.

“The security is very tight now, soldiers give the smugglers no respite,” said Abbas, 51, a farmer near the Turkish border town of Elbeyli, as two soldiers carrying rifles passed by his house, walking toward their outpost a few hundred meters away.

Last year, Abbas was so alarmed by the numbers of people crossing illicitly into Syria under his nose that he emailed a government bureau, set up years ago for citizens to register complaints, queries and concerns. It receives more than a million inquiries a year and Abbas said he never heard back.

“It was literally a flood of people here,” he said, describing how some in his village made a fortune shuttling people back and forth to the border fence, often doing a dozen trips a night, until the flow largely stopped about a month ago.

Several residents in other border villages and towns confirmed security had been tightened, but emphasized that did not mean the two-way traffic had dried up.

GRAPHIC - Areas of Syria controlled by government and rebel groups: reut.rs/1P61KRt

KILLINGS IN TURKEY

Turkey launched what it called a “synchronized war on terror” last July, opening up its Incirlik air base to countries in the U.S.-led coalition bombing Islamic State. Most of its own air strikes, however, have been against Kurdistan Workers Party (PKK) militants battling for Kurdish autonomy in its southeast.

Turkish tanks and artillery bombarded Islamic State positions in Syria and Iraq in the days after a suicide bomber blew himself up among groups of tourists in the heart of Istanbul last month, killing 10 Germans.

The security forces have also stepped up raids against Islamic State in cities across Turkey, detaining more than 1,000 alleged members and uncovering urban cells.

“We have never allowed Islamic State to use our territory to cross into Syria and we will not allow them ... We see Islamic State as an extremely serious threat and we don’t want them on our border,” a senior government official told Reuters.

Turkey has increasingly become a target itself for the Sunni Muslim radicals. The Istanbul bombing followed a suicide attack in Ankara in October that killed more than 100 people and a bombing in the border town of Suruc last July, both of which were blamed on Islamic State fighters.

Diplomats and analysts say Ankara woke up late to the threat, allowing Islamic State to develop networks of sympathizers, a charge the government rejects.

“These networks are tapped into well-established al Qaeda networks inside Turkey ... They were already there and they operated with little interference until March 2015,” Aaron Stein, senior fellow at the Atlantic Council said, nothing a marked increased in arrests thereafter.

Aside from the high-profile suicide bombings, Islamic State sympathizers have been able to carry out targeted attacks inside Turkish territory along the border in recent months.

Naji Jerf, a Syrian activist and documentary maker who made a film about Islamic State and had lived in Turkey’s southeastern city of Gaziantep since 2012, was gunned down on the street in broad daylight last December.

A couple of months earlier, two other Syrian activists who worked for Raqqa Is Being Slaughtered Silently (RBSS), a campaign group against Islamic State, were shot in the head and beheaded in the nearby city of Sanliurfa.

Jerf and the two activists had appealed to the Turkish police after they received death threats, friends and fellow activists in Istanbul and Gaziantep told Reuters.

“Naji went to the police after somebody tried to break into his car,” said his friend Manhal Bareesh, a journalist based in Gaziantep but originally from Syria’s Idlib province.

“He suspected they were trying to plant a bomb in his car. But the Turkish police wrote a report and told him not to worry,” Bareesh said.

Three people have been detained in Gaziantep in relation to Jerf’s murder, according to local media, but the killings have alarmed the Syrian immigrant community.