(Adds increased volume of a new issue) KYIV, Dec 11 (Reuters) - Ukraine increased its additional issue of Eurobonds maturing in 2033 to $600 million from $500 million, IFR reported on Friday, adding that investor demand exceeded $1.85 billion. Initially the country tapped the market with a yield target of around 6.4%, but later shifted it to 6.20%. Prime Minister Denys Shmygal said in early December that Ukraine could borrow about $1 billion on the external market by Dec. 15 as concerns over reforms have derailed a $5 billion loan deal with the International Monetary Fund. The government in July placed Eurobonds-2033 for $2 billion with a coupon of 7.253%.