US Secretary of State Hillary Clinton, who is on an official trip to Sofia Sunday, has met Bulgarian President Rosen Plevneliev.

Details from the meeting have not emerged, as Clinton has already entered another meeting, with PM Boyko Borisov and cabinet ministers.

A press-conference of Clinton and Borisov is scheduled after the meeting.

Among the items on the agenda are latest top security issues, including the nuclear program in Iran and escalating violence in Syria.

Matters in the military cooperation between the US and Bulgaria will also be discussed, both within the framework of NATO and bilaterally.

Bulgarian media have speculated that among the questions discussed is whether Bulgaria  will allow one of the US military bases in the country to be used for a potential strike against Iran, after Turkey has refused to do the same.

Other matters of discussion relate to energy security, where Clinton is likely to press for the development of shale gas in Bulgaria, for which US energy company Chevron has an interest.

Chevron already had a shale gas exploration permit, but in mid-January the Bulgarian Parliament voted on a moratorium on shale gas exploration and production in the country due to environmental fears raised by citizens.

The Bulgarian diplomacy is also likely to raise the issue of a visa-free regime with the US, though it has said that a significant progress is not very likely.