"Everything is prepared and (the government) will act, if needed, with firmness, proportionality and unity", a government statement said.
Spain's interim prime minister, Pedro Sánchez, said the court's decision "confirms the defeat of a movement that fails to gain internal support and worldwide recognition".
The separatists were convicted of sedition over their role in an illegal independence referendum in 2017. The divisive issue has divided families and friends, but demonstrations had largely been peaceful until this week.
Divisions over a drive to split the northeastern region of Catalonia from Spain roiled the country in 2017, and re-surfaced on Monday when the Supreme Court sentenced nine politicians and activists to up to 13 years in jail.
But the sentences triggered violent protests for a second day on Tuesday, with thousands of people denouncing the decision as unjust.
But the gatherings turned into melees, with protesters hurling firecrackers and other objects at anti-riot officers and kicking temporary fences around the official buildings. "What they don't realise is that we are very angry and we will not stop". "It is terrible that Europe doesn't act", 60-year-old civil servant Beni Saball said at a Barcelona street protest, referring to those convicted.
The convicted Catalan leaders - most of whom were kept in custody on grounds of a flight risk for almost two years before the verdict - have grown into powerful symbols for the separatists.
"The leaders condemned today [Monday] represent the majority of political parties in Catalonia", Guardiola said in a press release done simultaneously through TV3, the BBC and AFP.
On Wednesday, thousands of people joined five large protest marches across Catalonia that were set to converge on Barcelona on Friday.
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That led to the suspect - whose name has not yet been released - handing over the keys to a red Mazda sedan. After leaving Roseville, they "traveled to unknown places in Northern California and ended up in Mt.
Feliu, a retiree who walked 20 kilometers (12 miles) from the northern town of Berga and asked to be identified only by his first name because of the delicate situation in Catalonia, said he didn't agree with the violence but saw it as a way of gaining attention.
A spokesperson for Catalonia's regional government, Meritxell Budó, said they sympathised and understood the anger of the protesters.
There are more separatist leaders wanted by Spanish law in Belgium, Switzerland, and Britain. "I think these are people who will end up isolated and they are not significant - not significant of the movement, which is peaceful and has democratic values".
Quim Torra, the president of Catalonia, said: "We will never give up on the right to self-determination".
The separatist movement hopes for just the opposite - that the guilty verdicts will unite their divided ranks and bring supporters onto the streets.
The protesters sang the Catalan anthem and shouted, "The streets will always be ours", "Independence", as well as slogans calling Spanish police "occupying forces" and urging them to leave Catalonia.
Police arrested one protester at the airport while 53 people were injured.
Police made 29 arrests in Barcelona, the Catalan capital, during a raging street battle Tuesday night.
The verdict is likely to be a central issue in the run up to the vote but "it is unlikely to substantially alter the electoral outlook unless the situation worsens significantly in the region", said Antonio Barroso, a political risk analyst with the London-based Teneo consulting firm.