The article refers to capital, 3. (countable) A city designated as a legislative seat by the government or some other authority, often the city in which the go

The article refers to capital, 3. (countable) A city designated as a legislative seat by the government or some other authority, often the city in which the government is located; otherwise the most important city within a country or a subdivision of it. not capitol, 2. (US) Any building or complex of buildings in which a legislature meets. [Definitions from English Wiktionary] Being a UK newspaper, the Guardian would probably use "Lithuanian parliament buildings" or similar if that's what they meant.