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 provincial government spokesman Dauod Ahmadi said the explosion occurred early Tuesday on a busy street outside a police station, wounding at least 26 people, including 10 police officers.

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 a shooting incident inside the U.S. Embassy's annex in Kabul killed an American citizen and another wounded another.

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.

In other violence, a local government official in Herat province said a passenger bus returning from a wedding hit a roadside bomb, killing 16 people, including 11 children.

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.”

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.

Some Afghan officials have hinted that a recent series of targeted assassinations of Afghan officials may have been coordinated in part by Pakistan, a charge Islamabad denies.