TIKRIT, Iraq (AFP) -Insurgents have launched deadly assaults on Iraqi and US forces in northern Iraq, killing at least 27 people, while security forces cracked down further south in Baghdad.

In the bloodiest attack Sunday, a suicide bomber detonated explosives hidden in an animal feed truck outside a police station near Tikrit, killing 12 policemen and prisoners and wounding 25 more people, the police area commander said.

Further north near the Syrian border, insurgents ambushed a bus carrying new recruits from the Iraqi border security force, gunning down eight of them.

The violence in northern Iraq served as a grim reminder that — while US and Iraqi forces are conducting an energetic new operation to stifle sectarian bloodshed in the capital — the provinces are far from safe.

Police Lieutenant Colonel Hur Baz said 12 people were killed when the bomb hidden in the feed lorry destroyed his headquarters in the town of Ad-Dawr, a hotbed of support for Iraq’s executed dictator Saddam Hussein.

Twenty-five people were wounded — including police, detainees and civilian visitors — and rescue teams were searching throught the rubble, he said.

“Mechanical shovels have been brought in to lever up the wreckage that has fallen, to rescue the dead and wounded. The rescue operation is continuing, and Iraqi and US forces are at the scene,” Baz said.

A smaller roadside bomb exploded further north in Saddam’s hometown of Tikrit itself, killing two bystanders, police said.

The border guards had signed up in the border town of Rabiaa and were heading south to their new base when gunmen raked their minibus with automatic weapons, killing all aboard, regional official Jassim Mohammed told AFP.

Separate attacks in the nearby provincial capital of Mosul killed five people, including three policemen, medical official Mohammed Ahmed said.

Members of the Iraqi security forces are prized targets of Sunni insurgent fighters opposed to Iraq’s Shiite-led unity government and its US sponsors.

Closer to the capital, in Diyala province, a US soldier was killed in a battle between his unit and insurgents, the military said in a statement.

In Baghdad, a joint Iraqi-US force pressed its drive into insurgent hotbeds in search operations aimed at disrupting illegal fighter networks and clearing districts that had become no-go zones during a year of bitter fighting.

The military said troops had arrested 140 insurgent suspects in and around the capital during the week to Friday and that two “joint combat outposts” — fortified urban bases housing Iraqi and US forces — had been built.

US Apache gunships patrolled in tight circles over eastern Baghdad, a day after fighters attacked one of the new posts in the Adhamiyah district, and were repulsed after a 40-minute gunbattle that left no American casualties.

The attack was a sign that the insurgents were ready to challenge US troops and the security doctrine of US General David Petraeus, who took command Saturday of around 140,000 multinational forces in Iraq.

On Sunday, the capital was relatively peaceful amid reports that Shiite militiamen loyal to radical cleric Moqtada al-Sadr have decided to lie low until the security operation is over.

Sadr’s Mahdi Army is blamed by the United States for many of the sectarian attacks by Shiites on Sunnis in the capital, but he retains close links to Prime Minister Nuri al-Maliki and seems to want to avoid confrontation.

The US death in combat operations in Diyala brought US military losses in Iraq since the March 2003 invasion to 3,113, according to an AFP count based on Pentagon figures.