"They want to dominate us; but with the help of God, the will of the people will prevail," said Michael Ajasin, a 94-year-old opposition party leader.
Wahab Sosunmu, a former civilian minister and current opposition leader called Abiola's death "ominous."
But an official at Nigeria's New York Consulate denied yesterday afternoon that Abiola had been shot.
"There is nothing of such nature that has happened. If something had happened, we would know about it," said the official, who would not give her name.
In Washington, State Department spokesperson Glyn Davies called on the Nigerian government "to thoroughly investigate the crime, diligently pursue these killers and...ensure they're identified and duly prosecuted."
The British government yesterday called for Abacha's government to promptly and thoroughly investigate the killings.
In a magazine interview recently, Kudirat Abiola said she had been targeted with death threats and spoke of being followed by suspicious men.
She was detained briefly in May for allegedly publishing material critical of the Abacha government, according to her daughter, who said her mother had nothing to do with the publications.
The military regime has been under intense international pressure to release Moshood Abiola and scores of other political prisoners jailed since Abacha's November 1993 coup.
Pressure increased in November after the Nigerian government executed playwright Ken Saro-Wiwa and eight other activists from Ogoniland after convicting them of murder.
Soon after Saro-Wiwa's execution, Hafsat Abiola convinced the Undergraduate Council to pass a resolution calling for University divestment from Nigeria.
Some 500,000 Ogonis live in an oil-producing area that many say has been wrecked by pollution from the oil industry, which brings in 90 percent of Nigeria's export earnings.
Human rights groups have denounced Saro-Wiwa's trial as a sham that was meant to quiet Ogoni demands for compensation.
--Ariel R. Frank contributed to the reporting of this story, which was also compiled with material from Associated Press wire dispatches.