An Afghan official says gunmen opened fire at travelers on a highway in Wardak province early on March 24, killing 13 people.
The attack occurred during a visit by President Ashraf Ghani to the United States and underscored persistent violence following the withdrawal of most U.S. and NATO troops from Afghanistan last year.
The Associated Press news agency cited Attahullah Khogyani, a spokesman for the provincial governor of the province southwest of Kabul, as saying gunmen shot at three vehicles including a bus headed south.
The AFP news agency, also citing Khogyani, suggested all 13 victims were passengers on the southbound bus.
It cited Mohammad Ali, deputy governor of neighboring Ghazni province, as saying the gunmen picked their victims and shot them one by one.
Khogyani said two other civilians were wounded in the attack at about 1 a.m. in the Sayad Abad district.
Most of the district is controlled by the Taliban, whose fighters often plant roadside bombs and attack passing security convoys.
In a separate incident in Ghazni, six children playing cricket were killed when explosives attached to a bicycle exploded nearby.
Deputy Governor Ali said nine other children were injured in the blast in the evening on March 23.
Ali said four men were killed in a separate attack in the Aab Band district when gunmen opened fire on their vehicle and that two soldiers were killed by a roadside bomb in the Khwaja Omar district.
Violence has increased recently as the weather warms up, and this year there are far fewer foreign troops to help counter an expected spring offensive by the Taliban.
The number of foreign troops rose into the tens of thousands in the years after the U.S.-led invasion to oust the Taliban from power following the September 11, 2001, terror attacks.
But NATO's combat mission formally ended in December and there are now about 9,800 U.S. troops in Afghanistan.
Ghani has asked for "flexibility" from the United States, which currently plans to reduce that number to 5,500 by the end of 2015 and to a "normal" embassy presence by the end of 2016.
Ghani has also requested that U.S. bases in the eastern city of Jalalabad and the southern city of Kandahar -- where the Taliban had their capital until 2001 -- stay open as long as possible.
Ghani and President Barack Obama are expected to discuss the U.S. military presence issue later on March 24 at the White House.
U.S. Defense Secretary Ashton Carter, who met with Ghani and Afghan Chief Executive Abdullah Abdullah on March 23, said the Obama administration would be asking Congress to fund Afghan security troop levels at "an end strength level of" 352,000 to at least 2017.
Carter said the "Afghan and coalition military commanders have jointly recommended this force size… to ensure that the security gains we've made together are lasting."
U.S. Secretary of State John Kerry and other officials also took part in the meeting at Camp David, in Maryland.
Carter said Washington maintains an "unwavering commitment to a strong and strategic partnership with Afghanistan."
Ghani took office in September, and Abdullah Abdullah became chief executive, under a power-sharing deal that ended wrangling over a presidential runoff that was marred by suspicions of widespread fraud.
Ghani replaced longtime President Hamid Karzai, whose relationship with the United States had become increasingly contentious.
The United States continues to use drones to attack insurgents in Afghanistan and a report said a drone strike killed nine Pakistani militants in Afghanistan's eastern Nangarhar Province on March 24.
The strike hit near the site of fighting on the Pakistani side of the border, where Pakistan's military has been conducting an offensive against militant forces.
With reporting by AP, AFP, Reuters, and dpa