Speaking in the Oval Office before meeting with Borisov and the rest of the visiting Bulgarian delegation, Obama said the Balkan nation "has proven to be one of our most outstanding NATO allies."
"I've had an opportunity to work and discuss issues with the prime minister in the past, and he has always been a very effective leader on the world stage," Obama said before joking, "And I think it's important for everybody to know that he's also a black belt in karate, so you should be very careful crossing him."
He thanked the prime minister for Bulgaria's strong partnership in NATO. Obama said he and Borisov would "have a lot to discuss" but noted "Bulgaria has been a strong supporter of the efforts in Afghanistan, and we'll have the opportunity to touch briefly on the transition that needs to take place there."
"But I want to thank him and his fellow countrymen for their service and sacrifice," Obama said.
He also cited Bulgaria's "excellent cooperation" in anti-crime and anti-terrorism efforts, including a "very diligent investigation of the tragic terrorist attack that killed Israeli civilians in Bulgaria."
Borisov said it was an honor to be invited to the White House and he appreciated Obama's phone call after the July Hezbollah-linked suicide bomb attack in Burgas that killed six people, including five Israelis.
"I'm very glad that you pointed out that in countries such as Iraq and Afghanistan, places where our soldiers, U.S. and Bulgaria, fight for democracy shoulder to shoulder, that we do have additional topics of mutual interest," the prime minister said.
"As you know, a lot of Bulgarian soldiers perished and were seriously, grievously wounded in our missions in Iraq and Afghanistan. And the way that the U.S. people -- and you, personally -- protect the memory of the perished soldiers is unparalleled throughout the world."
Obama went on to call Bulgaria "a modernizing country" and "a leader in the Balkans in moving towards further integration with Europe and the rest of the world economy."
"We've been very impressed with the progress that's been made in Bulgaria, and I'm looking forward to hearing from the prime minister how the United States can further assist in those efforts," Obama said.
When it comes to economic matters, Borisov said, "It is true that Bulgaria is an island of stability in the Eastern Balkans. Our budget deficit is very low, our foreign debt is very low, and our financial stability is great."
He indicated Bulgaria's interest in diversifying its energy sources.
"We do have deep reserves in this area for the future," Borisov said.
"Of course, the Bulgarian citizens are expecting your decision on Bulgaria's joining the Visa Waiver Program. We do have visa-free travel regime with the entire European Union."
Notable deaths of 2014 [PHOTOS]
Cyclist struck and dragged underneath car