Afghan officials say a suicide car bomb attack has killed at least two people in Lashkar Gah, the capital of Afghanistan's volatile southern Helmand province.

The car bomb was detonated early Tuesday on a busy street outside a police station, wounding at least 26 people.

The Taliban has claimed responsibility for the attack.

Lashkar Gah was one of seven areas where control of security passed from foreign to Afghan forces in July as part of the first wave of a transitional process that is due to see all foreign combat forces leave Afghanistan by the end of 2014.

The attack comes one day after U.S. officials said an American citizen was killed and another wounded in a shooting incident inside the embassy's annex in Kabul.

A U.S. embassy spokesman said the incident took place Sunday night when an Afghan employee of the U.S. government opened fire on Americans before being killed himself. The NATO-led coalition force said early Tuesday the shooting happened “inside the embassy compound,” and said it was “not an attack.”

Meanwhile, hundreds of demonstrators gathered in Kabul Tuesday to call for an international investigation into last week's assassination of former president Burhanuddin Rabbani, who was leading the nation's peace negotiations with the Taliban.

The protest was led by former intelligence chief Amrullah Saleh, who stepped down last year after opposing the government's efforts to hold talks with the Taliban.

Many of the demonstrators held signs saying, “Death to the Taliban” and “Death to Pakistan.”

Some Afghan officials have hinted that the recent string of targeted assassinations of Afghan officials may have been coordinated in part by Pakistan.

Mr. Rabbani was killed a week ago at his home in Kabul by a suicide bomber pretending to deliver a “message of peace” from Taliban leaders.