A series of car bomb attacks and clashes between security forces and militants around and north of Baghdad killed at least 21 civilians, officials said Sunday, amid an ongoing standoff between Iraqi forces and al-Qaeda-linked militants west of the Iraqi capital.

The deadliest blast occurred at a bustling bus station in central Baghdad when an explosives-laden car exploded outside, killing at least nine people and wounding 16, a police officer said. Thousands of people use the bus station every day or pass through the area. Last Thursday, a suicide bomber blew himself up among a group of security force recruits nearby, killing nearly two dozen.

Another parked car bomb targeted a gathering of buses and taxis in Baghdad's northern Hurriyah neighbourhood, killing four civilians and wounding 12, the same police officer said.

Shortly after sunset, fighting erupted in Baghdad's western suburbs of Abu Ghraib as gunmen attacked a military convoy, authorities said. Army artillery shells later landed on the Sunni village of al-Mahsna in Abu Ghraib, killing five civilians and wounding 13, police said.

Later, a suicide car bomb exploded in the northern town of Tuz Khormato, followed minutes later by bomb hidden in a cart nearby, Mayor Shalal Abdoul said. He said the blasts killed three people and wounded 27.

Medical officials confirmed the casualty figures for all attacks. All officials spoke on condition of anonymity as they were not authorized to release the information.

The attacks come as Iraqi security forces and allied Sunni tribal militias in Anbar have been battling al-Qaeda-linked militants from the Islamic State in Iraq and the Levant.

Militants control Fallujah, Ramadi

Iraqi forces have yet to militarily try to reassert control over Fallujah, which remains in the hands of the militants and tribal gunmen opposed to the central government. Militants and tribal fighters also control part of the provincial capital, Ramadi. Sporadic clashes there and in surrounding areas continue to take place.

Thousands of families have left the area, fearing a government offensive. Clashes between militants and security forces have killed least 60 people since the violence erupted after the Dec. 28 arrest of a Sunni lawmaker sought on terrorism charges and the dismantling of an anti-government Sunni protest camp in Ramadi.

The extremist militants, emboldened by fellow fighters' gains in the civil war in neighbouring Syria, have tried to position themselves as the champions of Iraqi Sunnis angry at the Shia-led government over what they see as efforts to marginalize them.

At least 60 people have been killed since violence erupted in the western province after the Dec. 28 arrest of a Sunni lawmaker sought on terrorism charges and the dismantling of an anti-government Sunni protest camp in Ramadi. The head of Anbar's Health Directorate, Khudeir Shalal, said Saturday that 43 people were killed in the city of Ramadi and another 17 were killed in Fallujah. He added a total of 297 people were wounded in both cities.

In a sign of American concern over the situation in Anbar, Deputy Assistant Secretary for Near Eastern Affairs Brett McGurk wrapped up a three-day visit to Iraq to meet with Prime Minister Nouri al-Maliki and other top Iraqi political leaders, as well as tribal leaders from Anbar, to discuss the security situation.

U.S. promises weapons

In a statement, the U.S. embassy to Baghdad said that McGurk emphasized that the U.S. "will provide all necessary and appropriate assistance to the Government of Iraq ... under the Strategic Framework Agreement to help ensure that these efforts succeed."

Washington has ruled out sending American troops back in but recently delivered dozens of Hellfire missiles to help bolster Iraqi forces. It has promised to send more missiles as well as surveillance drones.

Other senior American officials have reached out to top Iraqi leaders too, with Vice-President Joe Biden speaking to al-Maliki twice last week alone.

Political tensions and violence have escalated in Iraq over the past year. Last year, the country saw the highest death told since the worst of the country's sectarian bloodletting began to subside in 2007, according to United Nations figures. The UN said violence killed 8,868 last year.

The U.S. Embassy also said McGurk visited Friday with members of Mujahedeen-e-Khalq, the militant wing of the National Council of Resistance of Iran, whose camp outside Baghdad came under rocket attack last month. The statement said the U.S. diplomat stressed the urgency of relocating the residents of Camp Hurriya to another country.

The dissident group, which opposes Iran's clerical regime, joined forces with Saddam Hussein's forces during the 1980-88 Iran-Iraq war, and several thousand of its members were given sanctuary in Iraq. It renounced violence in 2001, and was removed from a U.S. terrorist list last year.

Iraq's current Shia-led government, which has strong ties with neighbouring Shia powerhouse Iran, considers the MEK's presence in Iraq illegal and is eager to get rid of them. The refugee camp is home to about 3,100 people.