Bulgaria's army stepped in on Tuesday to buttress the southwestern border with Macedonia, which has been hit in recent days by an unprecedented influx of migrants.

Twenty-five soldiers and light armored vehicles will be deployed at Bulgaria's four border checkpoints with Macedonia, a defense ministry operations and training deputy chief told public BNR radio.

Bulgaria said Friday it was ready to dispatch its armed forces to secure its southwestern borders with Greece and Macedonia against any fresh influx of refugees.

The announcement came after Macedonia declared a state of emergency and closed its border with Greece because of large numbers of migrants trying to cross. 

Bulgarian prosecutors on Thursday charged 14 Muslim Roma with inciting racial hatred and spreading the ideas of the Islamic State jihadist group.

The charges come a day after the minority community's self-declared spiritual leader  -- controversial Roma imam Ahmed Moussa Ahmed -- was jailed for two years in another trial for propagating "anti-democratic ideals" and inciting hatred on religious grounds.

A controversial Bulgarian imam was sentenced to two years in prison Wednesday for propagating "anti-democratic ideals" and inciting hatred on religious grounds.

Ahmed Moussa Ahmed is the only one of 13 Muslim clerics charged with spreading radical Islamist propaganda to be sentenced to prison.

Bulgaria's prime minister appealed for calm Tuesday following several days of violence and ethnic tensions involving the EU country's 10-percent Roma minority.

"I call on everybody to be careful and not to play with fire... It is very easy to spark an ethnic conflict," Boyko Borisov told journalists, adding there was already "huge instability".

A U.S. defense contractor killed in a blast in Bulgaria last week was working for a program to train and equip Syrian rebels fighting against Islamic State, U.S. officials said Wednesday.

The American died when a rocket-propelled grenade misfired at a military range in Anevo in central Bulgaria on Saturday. 

Bulgaria, Greece and Turkey agreed on Monday to set up a common border police and customs center to combat a surge in illegal migration.

"This agreement guarantees closer cooperation of the three countries that face one and the same challenges... migration, organized crime and terrorism," Bulgaria's Interior Minister Rumyana Bachvarova said after a signing ceremony in Sofia.

Three alleged Hizbullah suspects -- two of whom are accused in a deadly 2012 bombing targeting Israeli tourists in Bulgaria -- have been placed on a special U.S. terror watch list, Washington announced on Tuesday.

The State Department named Meliad Farah, Hassan el-Hajj Hassan and Hussein Atris as "specially designated global terrorists."  

Bulgaria's government on Tuesday sacked the head of the border police and 25 customs officials, as it struggles with a sharp rise in migrants trying to enter the EU member state.

"We have little reason to be proud regarding our struggle against illegal immigration and smuggling," said senior interior ministry official George Kostov as he announced the decision.

Bulgaria's parliament recognized for the first time on Friday the mass killings of Armenians in the Ottoman Empire a century ago, holding a minute's silence but avoiding the word genocide.

The special declaration approved by parliament in a 157-36 vote condemned the World War I killings as a "massacre" while highlighting the difference between the former Ottoman Empire and modern Turkey.