The action followed clashes between demonstrators and police on U.S. campuses and a blockade at Paris's Sciences Po university
The extent of the casualties was still unclear and British officials were working with Afghan police, the spokesman said.
General Ayoub Salangi, the deputy interior minister, said the bomber was riding a motorcycle. The bombing is the latest in a wave of attacks to hit Kabul as the majority of foreign combat troops withdraw from Afghanistan by the end of the year.