By Jonathon Burch
ANKARA (Reuters) - Turkey has shut its side of the last border crossing with Syria still controlled by President Bashar al-Assad's government, stepping up security following two deadly bombings this month.
Fifty-one people were killed when twin car bombs ripped through the Turkish border town of Reyhanli in the southern province of Hatay on May 11, deepening fears that Syria's civil war was dragging in neighboring states.
Turkey has accused Syria of involvement in the attacks, but Damascus has denied any role.
Turkish Prime Minister Tayyip Erdogan will visit Reyhanli on May 30, local media reported on Wednesday. Turkish President Abdullah Gul visited the town last week while Erdogan was on an official trip to the United States.
The prime minister's visit could stir up tensions in Reyhanli and the surrounding area where several anti-government protests have erupted since the attacks.
Customs Minister Hayat Yazici said the Yayladagi gate, some 90 km (55 miles) from Reyhanli, would remain closed for a month, during which only Turkish citizens arriving from Syria or non-Syrians transiting through Turkey would be allowed to cross.
Nobody would be allowed to cross from Turkey into Syria.
The gate was initially shut the day after the bombings to prevent the attackers from fleeing to Syria.
A Turkish official in the region said there would now be time to station bomb-detecting equipment at the crossing.
The Yayladagi gate is the only crossing along the 900 km shared border whose Syrian side is still controlled by Assad's government. All other crossings have fallen into the hands of rebels fighting to overthrow him.
The Yayladagi crossing serves as the main route to Syria's northwestern coastal area around Latakia, which has a large Alawite population. Assad is also Alawite, a minority sect that has dominated Syria for decades.
Turkey says it has detained 18 Turks in connection with the car bombings, 12 of whom are facing formal charges, and that among them were some of the main perpetrators, including the owner of the vehicles used in the attacks.
Foreign Minister Ahmet Davutoglu has said the perpetrators came from an old Turkish "Marxist terrorist organization" with ties to Assad's government. Officials say no Syrians have been arrested in connection with the bombings.
Ankara said some of the perpetrators had traveled close to Yayladagi after the bombings to try and slip into Syria.
Small protests against Turkey's aggressive stance on Syria have broken out in cities across the country, including Istanbul and the capital Ankara, where police fired tear gas at protesters over the weekend.
The demonstrators, led mainly by leftist groups, blame the government for the bombings because of its Syria policy. Turkey has become one of Assad's fiercest critics and is one of the rebels' main backers.
Residents in Reyhanli and border areas have expressed similar anti-government sentiment since the attacks, saying a lack of security along the border was allowing radical groups to enter their towns unchecked.
Local anger has also been directed at the Syrian refugee population in Reyhanli, where thousands have settled. Most Syrians in Reyhanli have been too afraid to venture outside their homes since the bombings with reports of some Syrians being attacked.
Hatay Governor Mehmet Celalettin Lekesiz said six Turks had been detained on Wednesday on suspicion of planning to stage bomb attacks on Syrian refugees in Hatay province.
There are some 400,000 Syrians now living in Turkey, with around half of them sheltering inside camps and the other half living with relatives or in rented accommodation across Turkey.
(Editing by Nick Tattersall and Mike Collett-White)