U.S. Secretary of State Hillary Clinton on Sunday paid a short visit to Bulgaria and discussed energy issues and military cooperation with Bulgarian Prime Minister Boyko Borissov. In a joint press conference together with Borissov, Clinton said she had a very productive meeting with the Bulgarian prime minister, and underscored the depth and range of the partnership between the two countries. She said Bulgaria and the United States had worked alongside around the world to address critical issues, from ensuring a successful transition in Afghanistan, keeping the peace in Kosovo, to diversifying and securing energy supplies. \"We are partners working to advance Bulgaria\'s energy independence and security, and to protect Bulgarian beautiful environment,\" Clinton said. Bulgaria in January decided to prohibit the U.S. Chevron Corporation from making oil and gas exploration in the country by using hydraulic fracturing. Addressing Sunday\'s press conference, Borissov said the U.S. and the Bulgarian government would present the best new technologies to Bulgarian people, and that they would convince the public of their safety. Until then, the moratorium on exploration and production of shale gas in Bulgaria would be a fact. \"I would say the same for nuclear energy,\" Borissov added. In the meantime, Clinton described Bulgaria as an extremely important, productive partner of the NATO, and said her country was committed to Bulgarian security and was looking to expand its military collaboration with Bulgaria. She said they were looking for ways to deepen military cooperation and carry out a comprehensive review of what the status quo of this cooperation was, and where it would go in the future. In 2006, the United States gained military access to four Bulgarian military facilities, including two air bases. In 2011, Bulgaria said it was ready to host the future NATO missile defense system. Asked to comment on the situation in Syria, Clinton said the U.S. would increase the diplomatic pressure on the Assad regime, and work with the friends of the democratic Syria around the world to support the opposition. Earlier on Sunday, Clinton also met with Bulgarian President Rosen Plevneliev.