Sunnis and Shiites generally live in harmony in the country, but tit-for-tat attacks by militants from both sides have claimed thousands of lives in the last two decades.

The monitoring groups would also provide a confidential forum where the parties could work to restrain violent flare-ups, rather than engaging in escalating tit-for-tat attacks.

The 30th month of warfare around the capital has boiled down to a cycle of tit-for-tat attacks on supply roads on the city's periphery.

Second, the last week's fighting largely seemed to be a matter of tit-for-tat attacks.

Assassinations and tit-for-tat attacks followed, bringing the death toll up to 800 in the first seven months of this year.

The challenge came at the close of a week in which Mr. Kerry and Mr. Bush traded tit-for-tat attacks.

This incident raised awareness that the violence in Syria was heading towards an inexorable vicious cycle of tit-for-tat attacks between the different parties involved.

Eleven villagers were reported killed today in the latest flare-up of tit-for-tat attacks that have raised fears of a resurgence of ethnic violence here.

That killing, more typical and less alarming to ordinary Japanese, provoked the tit-for-tat attacks that led to the officer's death.

Similar tit-for-tat attacks wrecked all previous attempts at establish a cease-fire, and any such effort would be extremely fragile.