KABUL, Afghanistan (CNN) -- Nine U.S. troops were killed Sunday in an attack on a base in a remote province of eastern Afghanistan, a Western official said.
A U.S. Marine patrol Helmand province Sunday, where suicide bombings have recently become commonplace.
It was the deadliest attack on U.S. troops in Afghanistan in three years.
NATO confirmed that nine of its International Security Assistance Force troops were killed, but it didn't release the troops' nationalities. Fifteen other ISAF troops and four Afghan troops were wounded, NATO said.
"The fighting began in early morning hours and continued into the day as insurgents were repulsed from an Afghan National Army and ISAF combat outpost," said a NATO statement.
The statement continued, "Although no final assessment has been made, it is believed insurgents suffered heavy casualties during several hours of fighting."
Though details of the attack were sparse, an earlier statement from ISAF said Afghan and ISAF soldiers were involved in "heavy fighting" with insurgents at a command outpost in Kunar province.
"Insurgents have been firing at the [command outpost] with small arms, machine guns, rocket-propelled grenades and mortars, using homes, shops and the mosque in the village of Wanat for cover," according to the statement.
ISAF and Afghan soldiers, backed by air support, responded with small arms, machine guns, mortars and artillery, the statement said.
Since the start of coalition operations in Afghanistan, 470 U.S. troops have died. This figure includes Sunday's casualties.
News of the dead U.S. troops came after a suicide bomber riding a motorcycle killed at least 21 people, including four police officers, in southern Afghanistan Sunday.
The latest incidents are part of a deadly wave of weekend attacks that also included a suicide attack at an army camp in Helmand province and the death of two coalition soldiers.
The motorcycle attack occurred in the southern Afghanistan city of Tarin Kowt on Sunday, Afghan Defense Ministry spokesman Gen. Mohammad Zahir Azimi said.
The suicide bomber blew himself up in a market, authorities said.
Helmand province was the site of a deadly suicide attack by a teenager Saturday. Authorities said the teen detonated his explosives-laden vest outside an Afghan National Army camp. The blast killed the bomber and three others, officials said.
The boy approached the army camp in the Marja district. A soldier discovered the vest while searching the teenager, but it detonated immediately, ISAF said.
The blast killed the teen and two soldiers. A child later died of his injuries, ISAF said.
In other developments:
• Also in Helmand province, a coalition member was killed in a roadside bomb Sunday, the U.S. military said. The identity and nationality of the soldier was not disclosed.
• In northern Afghanistan on Saturday, a soldier assigned to ISAF was killed in an explosion. The soldier's nationality was not released.
• The Indian Embassy in Afghanistan will resume issuing visas on Monday, a week after a massive bombing outside its gates killed 58 people. An embassy staff member said maintenance work at the offices was almost complete. The suicide car bomb detonated July 7 in a crowded street outside the embassy, where dozens of people were lined up to apply for visas.
• Also in Helmand province, Afghan National Security Forces and coalition troops killed at least 40 militants in an ongoing operation, a coalition statement said. "Militants attacked an ANSF and coalition forces security patrol beginning [Saturday] in Sangin district, using small-arms fire and rocket-propelled grenades, from multiple concealed and fortified positions. The ensuing fight led ANSF and coalition forces to return fire and call for precision air strikes," the coalition statement said. "At least 40 militants have been killed in the last two days, while over 30 enemy boats and several hand bridges were also destroyed on the Helmand River."
CNN's Atia Abawi contributed to this report.