"What we realised and what we recognised over last four or five months is really an increase of incidents and accidents in the entire country," German Lieutenant General Norbert van Heyst told reporters at his monthly press conference at ISAF headquarters.

"Basically, the total number of incidents in May doubled against the number of incidents in April."

The level of attacks stabilised "on a very high level" in June, he said.

The US military, which heads an 11,500 strong coalition force in Afghanistan, has also acknowledged an increase in attacks in recent months.

A suspected bomber accidentally blew himself up Tuesday in a Kabul bazaar, police chief Basir Salangi said Wednesday.

In the deadliest attack yet on the peacekeepers, four German ISAF soldiers were killed and 29 others badly injured in a suicide car bomb attack on their bus on June 7 in Kabul.

Last week a US coalition soldier was killed in a firefight in southeast Afghanistan, bringing the toll of US troops killed in combat to 30.

A relentless campaign of attacks using mainly landmines, rockets and bombs is being waged against foreign and Afghan troops by rebels suspected of belonging to the Taliban, al-Qaeda and followers of renegade Islamist warlord and one-time premier Gulbuddin Hekmatyar.