'Yes, we yawn!' one local newspaper mocked Monday's mild face-off between Chancellor Angela Merkel and Foreign Minister Frank-Walter Steinmeier.
President Obama had hoped to pressure Iran by building international consensus on tougher sanctions.
The attack killed at least 19 people Thursday, two days after another bomb left three US soldiers dead. Insurgents may be moving north as coalition forces push them out elsewhere.
The US Mideast envoy called the meeting "good" but didn't say whether he discussed a settlement freeze, which Palestinians have called a prerequisite to peace talks.