Al-Shabab militants killed one US soldier and two American defense contractors during an attack at a Kenyan airfield used by United States forces Sunday morning.

The US military said in a statement that two Americans from the Department of Defense were also wounded in the attack.

'The wounded Americans are currently in stable condition and being evacuated,' the US military's Africa Command said.

Officials are not releasing the names of the victims until their next of kin have been contacted. There was no reported Kenyan deaths.

'Our thoughts and prayers are with the families of our teammates who lost their lives today,' said US Army General Stephen Townsend.

Townsend, who is the commander of the US Africa Command, said: 'As we honor their sacrifice, let's also harden our resolve. Alongside our African and international partners, we will pursue those responsible for this attack and al-Shabab who seeks to harm Americans and US interests.'

'We remain committed to preventing al-Shabab from maintaining a safe haven to plan deadly attacks against the US homeland, East African and international partners,' Townsend added.

Kenyan authorities said the pre-dawn attack also destroyed US aircraft and vehicles.

Scroll down for video

Al-Shabab militants killed one US soldier and two American defense contractors during an attack at a Kenyan airfield (pictured) used by United States forces Sunday morning

The US military said in a statement that two Americans from the Department of Defense were also wounded in the attack (pictured). 'The wounded Americans are currently in stable condition and being evacuated,' the US military's Africa Command said

Officials are not releasing the names of the victims until their next of kin have been contacted. There was no reported Kenyan deaths

The al-Qaeda-linked al-Shabab, based in nearby Somalia, claimed responsibility and asserted that 'intense' combat with US forces continued.

It is the first known al-Shabab attack against US forces inside Kenya, a key base for fighting one of the world's most resilient extremist organizations.

A plume of black smoke rose above the base. Residents said a car bomb had exploded.

Lamu county commissioner Irungu Macharia said that five suspects were arrested and are being interrogated.

An internal Kenyan police report seen by the Associated Press said two fixed-wing aircraft, a US Cessna and a Kenyan one, were destroyed along with two US helicopters and multiple US vehicles at the Manda Bay military airstrip.

The report said explosions were heard at around 5.30am from the direction of the airstrip. The scene, now secured, indicated that al-Shabab likely entered 'to conduct targeted attacks,' the report said.

A plume of black smoke (pictured) rose above the base. Residents said a car bomb had exploded

Lamu county commissioner Irungu Macharia said that five suspects were arrested and are being interrogated. Black smoke rises from the base following the attack

Sunday's attack is the first known al-Shabab attack against US forces inside Kenya, a key base (file image) for fighting one of the world's most resilient extremist organizations

According to the US military, 'initial reports reflect damage to infrastructure and equipment'. The Kenya Civil Aviation Authority said the airstrip was closed for all operations.

Al-Shabab's statement included photos of blazing aircraft it asserted were from the attack. A second al-Shabab claim issued hours later asserted that 'ïntense close-quarters combat' against US forces continued.

The military's Camp Simba in Lamu county, established more than a decade ago, has under 100 US personnel, according to Pentagon figures. US forces at the Manda Bay airfield train and give counter-terror support to East African partners, according to the military.

A US flag-raising at the camp in August signaled its change 'from tactical to enduring operations,' the Air Force said at the time.

According to another internal Kenyan police report, dated Friday, a villager that day said he had spotted 11 suspected al-Shabab members entering Lamu's Boni forest, which the extremists have used as a hideout. The report said Kenyan authorities did not find them.

Al-Shabab has launched a number of attacks inside Kenya, including against civilian targets such as buses, schools and shopping malls.

The group has been the target of a growing number of US airstrikes inside Somalia during President Donald Trump's administration.

The latest attack comes just over a week after an al-Shabab truck bomb in Somalia's capital killed at least 79 people and US airstrikes killed seven al-Shabab fighters in response.

Last year al-Shabab attacked a US military base inside Somalia that is used to launch drone strikes. The extremist group also has carried out multiple attacks against Kenyan troops in the past in retaliation for Kenya sending troops to Somalia to fight it.

This attack marks a significant escalation of al-Shabab's campaign of attacks inside Kenya, said analyst Andrew Franklin, a former US Marine and longtime Kenya resident.

The latest attack comes just over a week after an al-Shabab truck bomb in Somalia's capital killed at least 79 people and US airstrikes killed seven al-Shabab fighters in response. Pictured is the scene of the car bomb on December 28

'Launching a deliberate assault of this type against a well-defended permanent base occupied by (Kenya Defense Forces), contractors and US military personnel required a great deal of planning, rehearsals, logistics and operational capability,' he said.

Previous attacks against security forces have mainly been ambushes on Kenyan army or police patrols.

The attack comes days after a US airstrike killed Iran's top military commander. Iran has vowed retaliation, but al-Shabab is a Sunni Muslim group and there is no sign of links to Shiite Iran or proxies.

Analyst Rashid Abdi in Twitter posts discussing the attack said it had nothing to do with the tensions in the Middle East but added that Kenyan security services have long been worried that Iran was trying to cultivate ties with al-Shabab.

'Avowedly Wahhabist Al-Shabaab not natural ally of Shia Iran, hostile, even. But if Kenyan claims true, AS attack may have been well-timed to signal to Iran it is open for tactical alliances,' he wrote, adding that 'an AS that forges relations with Iran is nightmare scenario'.

When asked whether the US military was looking into any Iranian link to the attack, US Africa Command spokesman Col Christopher Karns said only that 'al-Shabab, affiliated with al-Qaida, has their own agenda and have made clear their desire to attack US interests'.

The al-Shabab claim of responsibility said Sunday's attack was part of its 'Jerusalem will never be Judaized' campaign, a rarely made reference that also was used after al-Shabab's deadly attack on a luxury mall complex in Kenya's capital, Nairobi, in January 2019.