Spanish opposition parties have stepped up their attacks on the socialist prime minister, Pedro Sánchez, as he prepares to announce whether he will resign because of what he describes as a “harassment and bullying operation” being waged against him and his wife by his political and media enemies. Sánchez shocked Spain on Wednesday night when he published a letter announcing that he would abandon his public duties for five days while he weighed up whether to step down, adding that he would reveal his decision on Monday. Earlier on Wednesday, a Madrid court had said it had opened a preliminary investigation into Sánchez’s wife, Begoña Gómez, “for the alleged offence of influence peddling and corruption”. The investigation followed a complaint from the pressure group Manos Limpias (Clean Hands), a self-styled trade union with far-right links that has a long history of using the courts to pursue those it deems to be acting against Spain’s democratic interests. In his letter, Sánchez said the Manos Limpias complaint was based on “alleged reporting” by news sites whose political leanings he described as “overtly rightwing and far right”, adding: “As is only logical, Begoña will defend her honour and will cooperate with the justice system as much as is necessary to clear up facts that are as scandalous in appearance as they are nonexistent.” Sánchez accused his political opponents – chiefly Alberto Núñez Feijóo, the leader of the conservative People’s party (PP), and Santiago Abascal, the leader of the far-right Vox party – of “collaborating with a far-right digital galaxy and with Manos Limpias”. Although more than 12,000 people rallied outside the socialist party’s Madrid headquarters on Saturday to show their support for the prime minister, opposition parties have only doubled down on their attacks, accusing Sánchez of cynical manoeuvring, melodrama and self-obsession. “We citizens shouldn’t be the ones focusing on Sánchez’s navel; Sánchez should be focusing on the citizens,” Feijóo said on Saturday. “Mr Sánchez, the question isn’t whether being prime minister of Spain is worth it or not. The question is whether or not Spain deserves a prime minister like you.” Vox said the fact that Sánchez still had not resigned was “a democratic anomaly”, and that “Europe is asking itself how Sánchez can carry on being prime minister when his wife faces such serious allegations”. A poll commissioned by the PP and published on Saturday showed 54% of the 1,527 people surveyed believed the prime minister’s actions were a strategy to garner support before the Catalan regional election in a fortnight and the European parliamentary elections in June. It showed 56.4% thought Sánchez would not resign on Monday, while 21.2% said they believed he would subject himself to a confidence vote in parliament in an attempt to shore up his leadership. Manos Limpias has accused Gómez of using her influence as the wife of the prime minister to secure sponsors for a university master’s degree course that she ran. Despite the severity of its allegations, Manos Limpias admitted on Thursday that its complaint against Gómez could be based on incorrect media reports, adding: “If they are not true then whoever published them should take responsibility. But if they are not untrue, we understand that the judicial investigation should continue.” Meanwhile, the ultra-conservative, ultra-Catholic group Hazte Oír (Make Yourself Heard) lodged a new criminal complaint against Gómez for alleged influence-peddling on Thursday. Prosecutors in Madrid have already asked the judge to throw out the preliminary corruption investigation triggered by the Manos Limpias complaint. Sánchez’s colleagues and allies have rallied around him in recent days. In an interview with El País on Sunday, the environment minister, Teresa Ribera, said the attacks on the prime minister’s family had worn him down. “He’s despondent – these have been tough years,” she said. “He’s strong but anyone can end up at breaking point … Every one of us has found themselves in situations that are unpleasant for our relatives, partners, children or parents over the past few years, and Sánchez has always been extraordinarily attentive and caring. Although he’s always been very restrained, those in his inner circle have sometimes seen how the direct attacks on [his family] have affected him.” Messages of support have also been offered by prominent international leftwing leaders. Brazil’s president, Luiz Inácio Lula da Silva, said he had phoned Sánchez to show his solidarity with a man who had worked to make Spain a fairer, more prosperous and humane place. “Your strength and your role are important for your country, for Europe and for the world,” he said. The Colombian president, Gustavo Petro, said the “mud-slinging machine” driven by the Spanish far right was trying to destroy Sánchez’s family in order to stop his progressive policies. “Rightwing politics is about destroying people,” Petro said. “I offer the Spanish prime minister and his family my solidarity.” Nicolas Schmit, the lead candidate for the Party of European Socialists in the June elections, said: “Pedro has been the victim of vile attacks from the far right for a long time. I stand with Begoña, Pedro and their whole family.”