* Socialist leader hints at election by year-end
* Pressure on government growing after poor EU election result
* Political instability has thwarted reforms
* Rift in coalition over South Stream pipeline (Adds details, background)
SOFIA, June 6 (Reuters) - The head of Bulgaria's ruling Socialist party backed calls on Friday for an early election, setting the clock ticking on an unpopular minority government that looks increasingly unlikely to survive into next year.
Pressure has mounted on technocrat Prime Minister Plamen Oresharski's government since May's European parliament elections, which the centre-right opposition GERB party won by a bigger-than-expected margin.
The Socialists have been in power for a year, and their time in office has been dogged by months of street protests over corruption in the European Union's poorest country, and a series of parliamentary no-confidence votes.
If the government falls it would be second such collapse in two years after a GERB-led administration fell in February 2013.
The long period of political instability has thwarted any meaningful attempts at reform in the country of 7.3 million, such as tackling graft, cleaning up the judiciary and overhauling inefficient education and healthcare sectors.
On Thursday, the junior partner in the coalition government, the ethnic Turkish MRF, called for an election by the end of the year.
Socialist leader Sergei Stanishev said he would start consultations with partners and other political parties on when new elections should be held.
"I do not think that the idea for such vote to be in a year is appropriate. The election should not be delayed, given that there is a lack of stronger public support," he told reporters on Friday.
Stanishev dismissed opposition calls for a snap poll but at the same time hinted an election could take place within months. He said a "new parliament" should approve next year's budget, a process that must take place by the end of 2014.
Rifts have emerged between the Socialists and MRF, most recently over Bulgaria's refusal to stop work on the South Stream gas pipeline across the Black Sea, whose fate has become entangled in the dispute between the West and Russia over Ukraine.
The Socialists, many of whose core voters are pro-Russian, want the Russian-led project to continue, while the MRF said Bulgaria should not act without Brussels' support.
While new elections will end the current political stalemate, analysts say voters are likely to elect another fragmented parliament that could in turn produce another unstable coalition government.
Prime Minister Oresharski's government relies on the support of a hardline nationalist party to stay in power and pass laws.
The Socialists won just 19 percent of the vote in the May 25 election, while GERB won 30 percent. The result has prompted the opposition to call another no-confidence vote against the government, which will take place next week.
At Friday's press conference, Stanishev also proposed the introduction of compulsory voting to boost the credibility of Bulgaria's electoral process. (Reporting by Tsvetelia Tsolova and Angel Krasimirov; editing by Matthias Williams and John Stonestreet)