2 U.S. troops, 19 Afghans killed

• NEW: Unknown gunmen killed Afghan Supreme Court official in Kabul on Saturday, police say


• Two ISAF members killed Friday were American, U.S. official says


• Taliban claims responsibility for killing Americans Friday, 18 Afghan soldiers Saturday

Kabul, Afghanistan (CNN) -- Two American soldiers and at least 19 Afghans were killed in a spate of attacks in Afghanistan Friday and Saturday, some of which were claimed by the Taliban, officials said.

The violence began Friday, when a bomb explosion hit a convoy of NATO-led International Security Assistance Force troops.

Two American soldiers were killed in that blast, a U.S. defense official said Saturday on condition of anonymity.

ISAF, which also reported the attack but did not release the nationalities of the victims, said the attack happened in eastern Afghanistan.

The Taliban claimed responsibility. Spokesman Zabiullah Mujahid tweeted that a U.S. convoy had been targeted in Bagram district and claimed five Americans were killed.

On Saturday morning, 12 Afghan civilians who were clearing mines in southern Helmand province died in an attack, according to Omar Zwak, a spokesman for the provincial governor.

The civilians were defusing devices planted by the Taliban to target military tanks and vehicles in an area between Shorabak and Nad Ali districts of southern Helmand, he said.

Afghan security forces who arrived at the scene of the attack killed three of the militants and arrested four others.

The Taliban claimed responsibility for the attack and said those killed were soldiers and not genuine mine-clearers.

Judicial official shot to death

Unknown gunmen in Kabul killed Atiquallah Raufi, head of the Afghan Supreme Court secretariat Saturday morning, said Hashmat Stanikzai, spokesman for Kabul's police chief.

That afternoon, a suicide bomber targeted a bus carrying Afghan National Army personnel in the Guzargah area of Kabul on Saturday afternoon, said Sediq Sediqqi, a spokesman for the Afghan Interior Ministry.

Six army personnel were killed and 18 other people were injured, including two women bystanders, he said.

The Taliban spokesman, Mujahid, claimed responsibility for the blast in an e-mail.

He said that from now on, Taliban attacks against foreign and Afghan forces would be stepped up.

Kabul residents fear for safety

In the past couple of months, the Taliban have targeted many Afghan National Army buses and other vehicles.

Two days ago, a bus carrying army personnel to work was targeted by a suicide bomber. Five servicemen were killed and 12 more were injured.

After many attacks on army buses, especially during the morning and evening rush-hour periods, Kabul residents are worried. Some have called on the Afghan Defense Ministry to change the way it transports army personnel.

Hashmatullah, who witnessed Saturday's attack, said: "The Defense Ministry should stop using big buses to avoid being an easy target, and its personnel should use different routes to commute to work."

He said that this way the lives of both army personnel and civilians who are traveling on the same roads would be saved.

The Taliban issued a separate warning Saturday via Facebook to media critical of the group, saying "that from now on (the Taliban) will not stay silent and tolerate their actions and by using every possible way attacks will be carried out against them so immorality is annihilated from its root in our country."

U.S. combat role ends

The continuing violence comes as Afghan forces prepare to take on greater responsibility for ensuring the country's security as international forces transition to a supporting role.

At the end of December, U.S. forces will end their combat role in Afghanistan and instead focus on counterterrorism missions and training, advising and assisting Afghan troops.

Nonetheless, nearly 11,000 U.S. troops will remain in Afghanistan in the beginning of 2015. American forces will drop to 5,500 in 2016 and by 2017 the coalition will consolidate to Kabul.

Hagel: More U.S. troops than planned will remain in Afghanistan next year

CNN's Masoud Popalzai reported from Kabul and Laura Smith-Spark wrote in London. CNN's Jason Hanna contributed to this report.