The French far-right presidential candidate Marine Le Pen has postponed several campaign events because she is yet to secure the 500 endorsements from elected officials needed to qualify for the first round of the vote. Le Pen, the leader of the nationalist-populist National Rally, is lying second in the polls and is widely considered to be Emmanuel Macron’s most likely opponent in a second-round runoff on 24 April. But Le Pen’s team said on Tuesday she was postponing two events – a press conference on her education policy scheduled for Wednesday and a trip to the northern Somme region on Saturday – to try to drum up more signatures before the deadline in 10 days’ time. All candidates in France’s presidential race must secure the endorsement of at least 500 of the more than 40,000 MPs, MEPs, senators, regional councillors and mayors, from at least 30 different départements and overseas territories, before 6pm on 4 March. The requirement, introduced by Charles de Gaulle in 1962 with a threshold of 100, was meant to limit the number of candidates but has been widely criticised over concerns it may exclude popular candidates from outside the political mainstream. Le Pen released a video on Monday appealing to mayors to endorse her run and saying she was still 50 names short. According to the Constitutional Council, which receives and verifies the signatures, she has 393 – more than 100 fewer than necessary. The far-right leader told French radio her position was “democratically terrifying”, calling on mayors to endorse her if they “find it really extremely serious that someone who can win this election cannot, for administrative reasons, take part”. Le Pen’s far-right rival, the TV polemicist Éric Zemmour, has cancelled a planned trip to the Indian Ocean island of Réunion, insisting he was “not suspending my campaign but shrinking it, because we still do not have these endorsements”. Zemmour, who is only marginally behind Le Pen in the polls, has 350 signatures, while Jean-Luc Mélenchon, the leader of the radical-left France Unbowed, polling at 11%, is short of about 60 endorsements, according to the council’s latest list. The prime minister, Jean Castex, appealed to elected officials on Monday to endorse candidates, saying only 10,000 out of the 42,000 who were eligible had done so. “The act of endorsing a candidate is not automatically synonymous with political backing. It is also a democratic act,” Castex told MPs. He said he would meet local mayors’ associations to underline the importance of popular candidates being able to stand. Macron, who polls predict will win a second term regardless of whom he faces in the runoff, has yet to formally declare himself a candidate, having devoted the past days and weeks to frantic last-ditch diplomatic efforts to avert a war in Ukraine. He is expected to announce his candidacy next week. Analysts said on Tuesday that even if his hopes of preventing Russian tanks from rolling towards Kyiv were dashed, voters were likely to give him credit for having tried. “Even if he fails with the Russians, he will have emerged as leading the European effort,” Philippe Moreau Chevrolet, of the public relations firm MCBG, told Agence-France Presse, adding that the crisis had placed Macron at the centre of media attention and public debate and “completely removed the opposition from view”.