SOFIA (Reuters) -Bulgarian Foreign Minister Mariya Gabriel, of the centre-right GERB party, said on Sunday no agreement had been reached on forming a new government with the We Continue the Change (PP) party.

Gabriel agreed to try to form a government following the resignation of Prime Minister Nikolai Denkov of the PP party on March 5 to allow the GERB to lead the government for nine months, as agreed after last year's elections.

"There were three days of talks ... we say no to permanent new conditions," Gabriel told reporters in the capital Sofia.

Negotiations failed due to demands by the PP for the post of interior minister, Gabriel said, adding she will submit a letter to parliament on Monday saying she is withdrawing her candidacy for prime minister.

"GERB will not participate in negotiations for a second time," said Gabriel.

If a second candidate for prime minister from the two biggest parties fails to form a government, President Rumen Radev must name a third party that will propose a candidate. Failure would pave way for snap elections.

In elections last April, GERB came first, winning 69 seats in the 240-seat parliament. The bloc led by PP won 64 seats.

Under the constitution, the Bulgarian parliament does not have to dissolve prior to snap elections.

(Reporting by Stoyan Nenov in Sofia and Aleksandar Vasovic in Belgrade; Editing by Giles Elgood)