MADRID -Spain's lower house on Tuesday rejected an amnesty bill due to differences on its scope between the ruling Socialists and a Catalan separatist party, in a blow for Prime Minister Pedro Sanchez that illustrates his parliamentary fragility.

The bill, rejected by 179 votes to 171, will now return for debate in a parliamentary committee and could eventually be sent back for another vote in the lower house. The amnesty bill is set to define Sanchez's second term and has prompted large protests against it.

Catalan separatists Junts voted against the law after they failed to reach a last-minute deal with Sanchez's Spanish Socialist Workers' Party.

Junts wanted all exceptions related to terrorism to be removed from the bill since some of its politicians are currently under investigation by courts over alleged terrorism-related crimes.

The bill was put forward by the Socialists in exchange for support for Sanchez's new term in office from Catalan separatist parties Esquerra Republicana de Catalunya and Junts.

"Junts cannot participate in leaving all Catalan separatism exposed to the arbitrariness of the politicised Spanish judiciary," said lawmaker Miriam Nogueras. She said the current amnesty proposal was too selective and has loopholes.

But Sanchez's party had said that some crimes involving terrorism-related charges could not be pardoned.

The amnesty would cover all events related to the Catalan independence drive from 2012, including a symbolic vote held in 2014 and an independence referendum in 2017, which courts declared as illegal.

It is expected to benefit several hundred separatists as well as some police officers who stormed polling stations during the referendum.

Sanchez, who opposed an amnesty in the past and still rejects a referendum on independence, has argued that the bill seeks to foster reconciliation. The conservative opposition accused him of undermining the rule of law. REUTERS