Police opened fire in at least two places in Kathmandu and repeatedly fired teargas to disperse protesters marching just 1km from the palace.
Twelve of the injured were in a serious condition, some of them with bullet wounds, doctors said.
Mobile phone services were cut in the capital in an apparent attempt to stop activists communicating.
The clashes came as opposition leaders formally rejected the king's pledge to restore democracy, saying they will continue protests in defiance of Saturday's renewed shoot-on-sight curfew in the capital.
Authorities imposed a new eight-hour curfew on Saturday in the Nepalese capital as thousands of protesters again took to the streets denouncing the king's promises as too little, too late.
"The royal proclamation is a sham," many shouted as they defied orders to clear the streets.
Later, following a meeting of the seven-party opposition alliance, protest leaders said they had agreeed to formally reject the king's offer.
"The king in his royal proclamation has failed to address the issues of the seven party alliance's roadmap and the understanding reached with the Maoists," the alliance said in a joint statement.
"There is no way we can join the government and our general strike and peaceful protest will continue."
Earlier two opposition leaders were released by authorities after they were arrested during protests on Friday.
Jhala Nath Khanal and Bamdev Gautam, both of the Communist Party of Nepal, were driven by police to party headquarters on Saturday morning, the party said in a statement.
In a live address to the nation on Friday, Gyanendra said he was restoring political power to the people and asked the seven-party alliance spearheading the pro-democracy campaign to name a new prime minister.
The Nepal king has been accused
of trying to fool the people
"Executive power ... shall, from this day, be returned to the people," he said in the announcement broadcast on state television and radio.
Opposition leaders said they saw little in the speech to resolve the crisis, which began when the king seized power in February 2005, saying he needed to crush the Maoist insurgency that had made holding elections impossible.
"This is incomplete," said Minendra Risal of the Nepali Congress Democratic party.
He said the king had failed to mention the return of parliament and election of a special assembly to write a constitution.
Most opposition leaders want a constitution that would make the king a ceremonial figure or eliminate the monarchy entirely.
But they saw other problems too. Under the king's proposal, he would retain an undefined political role in a constitutional monarchy and apparently keep control of the military.
"This looks like another attempt by the king to fool the people," said Subash Nemwang of the Communist Party of Nepal. "It is a desperate attempt to save the regime."