OAKLAND — A man and woman were shot to death two blocks from each other in East Oakland in a six-hour period from Saturday evening to early Sunday, police said.

At one of the scenes police officers also were shot at but, none was injured.

The two victims — who were not acquaintances — were identified as Rita Cortez, 20, and Tomas Melero-Smith, 19, both of Oakland.

Investigators said they believe there was a definite gang link to Melero-Smith's killing and are trying to determine if the two cases are connected.

Both victims were standing with other people who were not hurt by the gunfire, police said.

Police said Melero-Smith was standing with two 18-year-old friends, whose names were not released, outside a house on the 2100 block of 94th Avenue about 6:53 p.m. Saturday.

A car with several people inside pulled up and one of the occupants got out, said a few words to the three men and began shooting at them as they tried to flee. Melero-Smith, who lived in the Fruitvale district, was the only one hit. He died at Highland Hospital at 10:14 p.m. Saturday.

Sgt. Tony Jones said he believes the people in the car were gang members who mistakenly thought Melero-Smith and his friends were rivals.

Cortez was shot about 11:38 p.m. Saturday on the 2100 block of 96th Avenue. She died at Highland Hospital at 12:27 a.m. Sunday.

Sgt. Jim Rullamas said Cortez, who lived in another part of Oakland, was with her 18-year-old boyfriend. They had just arrived at the site and were standing outside a house when a car drove by and someone inside the vehicle began shooting at them.

The boyfriend, whose name was not released, told police he tried to move Cortez out of the way of the gunfire. At least two bullets hit the house they were outside; no one else was injured.

Shortly after the first patrol officers arrived on the scene someone began shooting at them from more than a block away near 96th and Bancroft avenues.

The officers ducked for cover and "heard bullets whiz over our heads," Sgt. Jill Encinias said. Police searched the area, but did not find any suspects or other evidence, she said.

Police are not sure whether the shots fired atthem were connected to the Cortez case or because of something else.

Rullamas said police are not sure of a motive in the Cortez killing. But because of the circumstances and proximity to where Melero-Smith was killed, a gang link "is something we are considering," even though Cortez and her boyfriend are not gang members, he said.

Police and Crime Stoppers of Oakland are offering up to

$20,000 in reward money in each case for information leading to the arrest of the suspects. Anyone with information can call police at 238-3821 or Crime Stoppers at 238-6946.

The two killings were the third and fourth since Friday morning and brought the city's homicide tally for the year to 91. Last year at this time there were 98 homicides in Oakland.