Violence erupted on the streets of the Thai capital late Friday and early Saturday after a week of negotiations had raised hopes of a deal to end anti-government protests.
Leaders of the Red Shirt protest movement and Thailand's prime minister were considering a government proposal to hold new national elections in the fall, more than a year ahead of schedule.
But the overnight attacks in Bangkok threaten to jeopardize a peaceful end to the protests, which have paralyzed areas of the capital for nearly two months.
The latest violence killed two people and wounded 13 others.
In the first attack, a gunman on a motorcycle shot and killed a police officer just before midnight near the perimeter of the protest camp.
A second officer was killed around two hours later as three grenades exploded in the same part of the commercial core where similar attacks occurred just over a week ago.
Protest leaders denied Red Shirt involvement in the attacks and urged security forces be withdrawn from the streets, noting they only served as "lightning rods" for those trying to provoke violence.
Both the shooting and the grenade explosions occurred within two blocks of Bangkok's bar and tourist epicentre, Patpong Road.
The continuing violence and travel warnings issued by dozens of countries have thrown Thailand's tourism industry into a major economic depression.
The government warned protesters Saturday that more violence could erupt if the demonstrations do not end soon.
Government spokesman Panithan Wattanayagorn said that if the Red Shirts didn't end their occupation of Bangkok's prime commercial district "some people who don't wish to see reconciliation take place may take this opportunity to launch another attack."
He described the unknown assailants responsible for several attacks in the capital as "ill-intentioned people who used terror to try to ruin the conciliatory atmosphere."
Violence tied to the protest — including clashes between demonstrators and security forces — has killed 29 people and wounded nearly 1,000.