BAGHDAD – A tanker truck packed with explosives ripped through an Iraqi police outpost Monday, killing at least seven people in a suicide attack at a former insurgent stronghold west of Baghdad.

The blast outside Ramadi showed that Iraqi forces remain vulnerable — and now the primary target of insurgents — despite additional security measures imposed following devastating bombings in downtown Baghdad in August that killed about 100 people. Two months earlier, U.S. forces pulled out of Iraqi cities as part of its phased withdrawal from Iraq.

An Iraqi police official said the suicide attacker struck the outpost at midday in the desert north of Ramadi, about 70 miles (115 kilometers) west of Baghdad. At least 16 people were injured in the explosion, said the official.

Witnesses said the truck exploded near the front gate of the post, erupting into a huge fire ball and setting cars and trucks ablaze.

"It is like an earthquake took place ... because of the blast," a police officer said.

He said the blast also threw cars into the air and overturned trucks.

In a separate attack, at least three Iraqi soldiers were killed in a double roadside bombing in the predominantly Sunni neighborhood of Ghazaliyah in western Baghdad, said another police official. Fifteen others, including 11 civilians, were wounded, he said.

Both the police officials spoke on condition of anonymity because they was not authorized to release the information.

The news came as the U.S. military freed another 35 members of a group linked to the abduction of five British citizens from Iraq's Finance Ministry in 2007, a representative for the faction said.

The prisoner release means nearly 100 members of Asaib Ahl al-Haq, or League of the Righteous, have left U.S. custody since late last week. In total, about 250 have been freed since July as talks intensify over the fate of the sole British hostages believed to be still alive.

An envoy for the militant group, Salam al-Maliki, said the talks also are seeking the release of its leader, Sheikh Qais al-Khazali.

But negotiations are complicated by efforts to seek guarantees to free Peter Moore, the remaining hostage.

"We are trying to free (al-Khazali). His case is postponed for the time being," said the envoy al-Maliki.

A group of armed men seized Moore, a computer expert working for a U.S.-based consultancy firm, and his four bodyguards from the Finance Ministry in May 2007. The bodies of at least three of the hostages have been identified, but Moore is believed to be the only surviving captive.

Despite the decline in overall violence in recent years, the continued attacks have raised questions about the capabilities of Iraqi security forces to take over from withdrawing American forces.

In southern Iraq, bomb attached to a bus exploded in mostly Shiite southern Iraq, killing at least six, according to a police official.

In northern Iraq, a roadside bomb targeting a police patrol in Mosul killed two officers and wounded two, said another police official.

The two officials spoke on condition of anonymity for the same reason as the others.