TUNIS (Reuters) - Tunisian President Kais Saied said on Saturday that Tunisia would not accept becoming a border guard for other countries ahead of a planned visit by European leaders concerned at the number of migrants crossing the Mediterranean.

Italian Prime Minister Giorgia Meloni, Dutch Prime Minister Mark Rutte and European Union Commission Chief Ursula von der Leyen will offer aid when they visit on Sunday, Meloni said on Friday, with Tunisia facing a crisis in its public finances.

"The solution will not be at the expense of Tunisia... we cannot be a guard for their countries," Saied said while visiting the port city of Sfax, the main departure point for migrants seeking to reach Italy by boat.

Credit ratings agency Fitch on Friday downgraded Tunisian debt deeper into "junk" territory, underscoring the possibility it will default on loans, prompting a collapse in state finances that could cause widespread hardship.

European countries fear that would turbocharge what is already a big surge in cross-Mediterranean migration this year, particularly from Tunisia.

However, an IMF rescue package has been stalled for months with Saied rejecting the economic reforms needed to unlock the loans. Donor countries have been pushing him to change tack and Italy has urged the IMF to finalise the loan.

Perilous Mediterranean crossings soared after Saied announced a crackdown on sub-Saharan migrants in February using language the African Union denounced as racialised.

(Reporting by Tarek Amara, Writing by Angus McDowall; Editing by Andrea Ricci)