The opposition Union of Democratic Forces (UDF) decided not to run in the next general and European Parliament elections in coalition with its partner so far, the Democrats for Strong Bulgaria (DSB).
Following this decision, Martin Dimitrov resigned as UDF leader, state-run Bulgarian News Agency (BTA) said on Tuesday.
"I have been working to forge the unity of the right wing for three years and it would not be responsible and serious to say now that we have to run on our own in the next elections," BTA quoted Dimitrov as saying.
On Monday, DSB deputy chairman Radan Kunev told journalists that his party is ready to run the elections on its own if UDF decides to leave the Blue Coalition, adding that it has drafted an alternative economic programme.
The UDF and DSB set up the Blue Coalition ahead of the 2009 general elections.