(Adds Three Turkish citizens banned from Bulgaria)
By Tsvetelia Tsolova
SOFIA, March 17 (Reuters) - Bulgaria's caretaker prime minister said on Friday he was taking steps to prevent any attempts by Turkey to influence an election next week in favour of a political party that represents Bulgarian Turks, the country's largest ethnic minority.
The Balkan country's national security agency later said it had expelled a Turkish citizen and banned two others from entering the country over what it described as activities against Bulgaria's sovereignty and national unity. It did not give details.
Last week, the government summoned Turkey's envoy to Sofia after reports that a Turkish minister had campaigned for the DOST party in Istanbul, where many Bulgarian citizens live. Late on Thursday, it also recalled its own ambassador to Turkey for consultations. "It is true that there is a certain tension linked with one of the political parties, which is receiving support from the Turkish state, but we are taking measures that this does not continue," caretaker premier Ognyan Gerdzhikov told reporters.
Bulgarians will vote in a snap parliamentary election on March 26.
Seeking to downplay the tensions with Bulgaria's southern neighbour, Gerdzhikov said Turkey had tried to influence other Bulgarian elections since the fall of communism 26 years ago, and "now, there is nothing that is a way different".
More than 400,000 Bulgarian nationals live in Turkey, most of them Bulgarian Turks descended from Ottoman-era Turkish settlers in the Balkans. Bulgarian Turks are estimated to be more than half a million of Bulgaria's 7.2 million population.
Recalling an ambassador for consultations is a way of protesting that stops short of suspending diplomatic relations.
The move by Bulgaria's interim government, which has limited powers, follows a row between Ankara and The Hague in the run-up to this week's Dutch election which saw Turkish ministers banned from holding rallies in the Netherlands.
Other European Union countries including Germany have also angered President Tayyip Erdogan by barring campaigning among Turkish expatriates to drum up support for a referendum in April that would increase Erdogan's powers.
"The interim government is concerned that Turkey may create tensions that go beyond the normal diplomatic process, as it happened in the Netherlands," said Vessela Tcherneva, Sofia-based analyst with the European Council on Foreign Relations.
"The problem is that if Turkey presses on, the Bulgarian nationalists may try to block the border to prevent Bulgarian citizens from Turkey crossing into the country to cast their ballots, and that will create a scandal."
The spat with Turkey was credited with giving centre-right Dutch prime minister Mark Rutte a last-minute boost in the polls after an election campaign in which immigration and integration were key issues.
Opinion polls suggest the nationalist coalition United Patriots will come third in a tight race for the Bulgarian parliament and play a key role in forming the next government. Support for the party has grown as a result of Europe's migrant crisis.
DOST, which split from the traditional ethnic Turkish MRF party last year, is not expected to pass the minimum threshold to win seats.
EU member Bulgaria seeks to maintain good relations with Turkey, which it shares a 260 km border with and relies on to stem a possible increase in migrant inflows. Amid the rise in tensions with EU countries, Turkey's foreign minister said this week that Ankara may cancel a deal with bloc over migrants. (Editing by Catherine Evans)