(Corrects name of opposition leader in para 6 to Requesens from Requessens)
By Corina Pons and Andrew Cawthorne
CARACAS, April 5 (Reuters) - Venezuela's opposition's lawmakers gathered from dawn on Wednesday, some carrying injuries from protests, to seek the dismissal of Supreme Court judges whom they accuse of propping up a dictatorship.
Newly-militant opposition leaders also announced another round of demonstrations against socialist President Nicolas Maduro for Thursday, despite chaos and violence in Caracas on Tuesday that left 18 people arrested and 20 injured.
The opposition, which won control of the National Assembly in late 2015, accuses Maduro of wrecking the South American OPEC nation's economy and squashing democracy.
The political drama is playing out to the backdrop of a deep economic crisis, with Venezuelans suffering a fourth year of recession, widespread shortages of basic foods and medicines, the world's worst inflation, and long lines at shops.
Having been impeded from reaching the National Assembly on Tuesday, lawmakers headed to the building in downtown Caracas from daybreak on Wednesday, some with head-wounds or bandaged arms from the clashes of recent days.
"These injuries are nothing," said one lawmaker Juan Requesens, who received more than 50 stitches after being hit by a stone when pro-government supporters confronted protesters at the public ombudsman's office earlier this week.
"We are going to keep fighting for change, opposing the repression and the dictatorship, for Venezuela and for Venezuelans. We demand immediate elections," he added on his way into the session at 6.30 a.m.
The Penal Forum rights group said 18 people were still behind bars on Wednesday after a wave of detentions around the country but mostly in Caracas. At least 20 people were injured on Tuesday, its head Alfredo Romero told Reuters.
The head of the hemispheric Organization of American States and global rights group Amnesty International both condemned Venezuela for excessive repression.
But Interior Minister Nestor Reverol denied that, calling instead for one opposition leader, Henrique Capriles, to be prosecuted for blocking streets, including an ambulance.
"The exemplary behavior, capacity and training of our citizens' security organs prevented the unpredictable consequences of these terrorist groups," he added.
The South American OPEC nation's political standoff took a new twist last week when the Supreme Court ruled that it was taking over the legislature's functions.
That touched off an international outcry, and the tribunal quickly scrubbed the offending clauses.
But dozens of previous rulings overturning National Assembly measures have anyway left it powerless, and opposition leaders say recent events have shown the world Maduro's autocratic face.
Lawmakers were expected to approve a motion later on Wednesday asking for the removal of Supreme Court judges for "the breaking of Venezuela's constitutional order".
But that would anyway be symbolic only given they require the support of other institutions that are behind Maduro.
The president says his foes are seeking a coup with the connivance of Washington and compliant foreign media.
During an activity in rural Apure state, Maduro told supporters they were "in battle" against "imperialism."
"From the north, they have given the order to the defeated, fascist right wing to fill the streets of Venezuela with violence," he said late on Tuesday. "But peace triumphed."
Thousands of protesters had poured onto the streets of Caracas on Tuesday. Security forces using teargas and pepper-spray blocked them from reaching their rallying point.
Opposition leaders led demonstrators onto highways to block traffic, and some youths donned masks and tossed stones in skirmishes with police and soldiers around the city. (Additional reporting by Andreina Aponte; Writing by Andrew Cawthorne; Editing by Alistair Bell)