Dr Hasan al-Juburi, director of the Tikrit Teaching hospital, said the blast tore through the Sunubar Hotel at 8pm (1700 GMT) on Sunday.
Eight other people were seriously wounded in the explosion, including two policemen. All the victims were Iraqis, he added.
A police official confirmed the incident and said the explosion may have been caused by a projectile. He had no further details.
Tikrit, about 130km north of Baghdad, is the hometown of former leader Saddam Hussein.
Deaths in Ramadi
Earlier in the day, at least 10 Iraqis were killed and 15 people wounded, including three US marines, when fighting erupted between armed fighters and US troops in Ramadi, medics said.
A campaign of bombings has put
all government plans in disarray
In other incidents, a British soldier was found dead on a military base in Basra in the south, a military spokesman said, adding that the cause of death was not immediately known.
Meanwhile, a Sudanese working as an interpreter for a US company and truck drivers from Bangladesh, Sri Lanka and Somalia have joined Iraq's long list of captives.
Against this backdrop of escalating violence, interim Prime Minister Iyad Allawi has pledged to secure the country in the run-up to national elections promised by January and is ready to use force, if necessary, with the support of US-led forces.
Interim Prime Minister Allawi has
put 'foreign fighters' on notice
"We have entered the final phase to solve the Falluja problem," Allawi said in Baghdad on Sunday.
Since 14 October, US troops have encircled Falluja, where the military has repeatedly launched air strikes and some limited ground incursions.
At the same time, they are doubling their troop strength to 2000 in Ramadi.
A Falluja negotiator said the mujahidin shura (council) - a
body that says it represents at least some of the resistance forces in the city - along with local governors and tribal
shaikhs - had agreed in principle to restart talks provided the
US military halted daily air strikes.
Lieutenant-Colonel Hakim Karim Midab said local leaders would demand residents who had fled the fighting be allowed to return and be compensated for damage, and that US troops remove a checkpoint on the town's eastern entrance.
Midab said the city's leaders would also push for an Iraqi National Guard force that would include local residents to keep the peace between US forces and fighters in the town.
The US insists on attacking
Falluja, says the city's residents
But the interim Iraqi government has refused all negotiating points and insisted on the surrender of Abu Musab al-Zarqawi, whom the US has blamed for a string of deadly attacks and beheading of captives in Iraq.
Falluja residents, however, insist that al-Zarqawi is not in their town.
Nevertheless, Allawi laid down three conditions that, if met, would bring to a halt attacks on Falluja.
These include the exit of "foreign fighters", the handover of heavy and medium-sized weapons and allowing the government to begin the process of reconstruction in these cities.
"The people of Falluja can hand over the foreign fighters and insurgents, kick them out or allow Iraqi forces to go in and do the job," Allawi said.