Senior officials from the US and Iran are holding fresh talks on the security situation in Iraq, only their second bilateral meeting in 27 years.

The US envoy to Iraq, Ryan Crocker, and his Iranian counterpart, Hassan Kazemi-Qomi, are meeting in Baghdad.

The discussions are a follow-up to the ground-breaking talks held on 28 May.

The US blames Iran for supporting some of those who are attacking US and UK troops in Iraq, while Iran blames the US troop presence for Iraq's troubles.

The insurgency and related sectarian violence in Iraq are causing thousands of deaths every month.

Separate talks

The talks began with a heated exchange between the Iranian and US ambassadors, the Associated Press quotes an anonymous Iraqi official as saying.

Mr Crocker charged the Iranians with providing training and weapons to the Shia militias behind violence in Baghdad and beyond, the AP reports.

Mr Kazemi-Qomi reportedly brushed aside the allegations, saying that the US had no proof of its claims.

On Monday, Iraqi President Jalal Talabani held separate talks with the two ambassadors to urge them to work together to improve his country's security.

However, ahead of the talks, the US and Iran continued to blame each other for the situation.

US state department spokesman Sean McCormack said Tehran had not taken any steps to bring about a stable Iraq since the talks in May.

Mr McCormack said US intelligence showed Iran was continuing to stoke sectarian tensions and was still "providing assistance" to militias and death squads.

More than 200 US soldiers have been killed by armour piercing bombs, which the US says have been manufactured in Iran or made using Iranian-imported expertise.

"We are going to raise the need for Iran to match its actions with its words in seeking strategic stability in Iraq," he said.

"We'll see if, as a result of these engagements, they will change their behaviour."

The US has also said it believes Iran may have been implicated in the capture of five Britons who were taken hostage in Baghdad two months ago.

Differences

The Iranians, meanwhile, have called for the release of five of their citizens who were detained by US forces in Iraq in January.

The US has said they are members of the elite Quds Force of the Islamic Revolution Guard Corps (IRGC), but Tehran says they are diplomats.

The BBC's Nicholas Witchell, in Baghdad, says that despite all the differences between the US and Iran, neither country wants the turmoil in Iraq to continue unchecked.

Analysts say the atmosphere could also be more promising because Iran is trying to prevent a new round of sanctions threatened over its controversial nuclear programme.

The US broke off relations with Iran in 1980 when Islamic revolutionaries seized the US embassy in Tehran and held many diplomats hostage.