BAGHDAD — Insurgents have in Iraq stepped up deadly gun attacks against senior officials and military leaders in a bid to undermine public trust in the security forces, officers and analysts said on Sunday.

The apparent trend is a major shift from the spectacular car bombs and suicide attacks that Al-Qaeda, which have been blamed for a recent spate of targeted killings in Baghdad, appeared to focus on in 2009 and much of 2010.

In recent days, however, three top officials have been shot dead with silenced guns in the Iraqi capital, leading to tighter security at checkpoints, with officers checking pistols to see if they can be fitted with silencers.

"Al-Qaeda are moving to these kinds of attacks because they cost them less money and less effort, but they have a large impact on state institutions," a senior anti-terror police officer told AFP, speaking on condition of anonymity.

On Friday, a senior official in Iraq's foreign ministry was shot dead in north Baghdad and a police departmental chief was wounded by men using silenced pistols.

In separate incidents a day later, the head of Iraq's tax agency and an army lieutenant colonel were killed -- again by gunmen using silencers.

On Thursday, meanwhile, the Islamic State of Iraq, Al-Qaeda's front group in Iraq, posted a statement on the Internet jihadist forum Honein, claiming to have carried out 62 "operations" from the beginning of March until April 5.

ISI said it had been primarily targeting military officers and top ministerial officials using silencers, snipers and magnetic "sticky bombs" that attach to vehicles.

"Al-Qaeda are under siege because of security measures that make it difficult for them to move freely from one place to another," said the senior police officer.

"They cannot transfer explosive materials because of security at checkpoints and these transfers require money, which they lack."

He added: "Sometimes, Al-Qaeda know their target but other times they don't know who they have killed -- they are just targeting cars that belong to the government."

That view was supported by Iraq's deputy national security adviser Safa Hussein, who told AFP in an interview in January that "some of the (Al-Qaeda) cells target government cars. When they see a government car, they kill the person inside it."

He noted at the time: "One of the strategies of Al-Qaeda to disrupt the government is by assassinating officials who work in the government."

The latest string of targeted killings comes as security forces in Baghdad have tried to loosen restrictions in the city by opening up new roads, taking down blast walls, removing checkpoints and reducing an overnight curfew from five hours to three.

"Rather than concentrating on spectacular attacks, these recent operations are trying to undermine the trust of the civilian population in the security forces," said Ihsan al-Shammari, a Baghdad-based analyst.

"Targeting senior officials and leaders has an effect on the street, especially because officials have their own security protection."

The latest violence comes with just months to go before a year-end deadline for the fewer than 50,000 US troops currently in the country to withdraw, under the terms of a bilateral security pact.

Violence has dropped off dramatically across Iraq since its peak in 2006 and 2007, when tens of thousands were killed in nationwide sectarian bloodshed. But attacks remain common, especially in the capital.

A total of 247 people died in violence in Iraq in March, according to official figures.