A ceremony on Friday marking the occasion was attended by Kenyan President Uhuru Kenyatta, Ugandan President Yoweri Museveni, Rwandan President Paul Kagame and Ghanaian President John Dramani Mahama.
Kenyatta, for his part, used the occasion to reflect on a string of attacks in the country that had left more than 300 people dead since last year.
He said Kenya had experienced a number of "serious terrorist" attacks that had killed hundreds of citizens and injured hundreds of others.
"Despite these attacks, we are undeterred and remain steadfast in our commitment to the war on terrorism," Kenyatta said in a televised address from southern Nairobi's Nyayo Stadium.
"Insecurity in our country has both local and international dimensions," he stressed.
He added that the global war on terror had forced Al-Qaeda and its affiliates to seek safe havens for training and opportunities to pursue illegal economic activities.
The Kenyan president said that Al-Qaeda and its affiliates had found refuge in Somalia, describing the troubled country in the Horn of Africa as a "vulnerable host" with which Kenya shares a long and porous border.
Ordinary Kenyans, too, attended the ceremony, filling some 30,000 seats of the stadium.
Kenyatta went on to remind Kenya's international partners that the country was fighting a "proxy war" on behalf of all nations and peoples who embraced freedom and democracy.
"For this reason, we deserve and expect support, solidarity, and a more robust engagement in connection with our fight against terrorism," Kenyatta said.
"It's clear that our security system requires enhancement to confront the twin challenges of domestic and international security threats," he stressed.
He went on to say that his country was confronting "highly-trained" and "dangerously armed" militants, adding that Kenya's security apparatus ought to be able to curb the emerging insecurity.
Nevertheless, he stressed, "Kenya must enhance its ability to detect, monitor and eliminate security threats."
"It must also possess the forensic capacity to successfully prosecute terrorists," he added to intermittent applause.
He said the Kenyan government had embarked on a long-term strategy aimed at bringing Kenya's national security up to international standards.
Kenyatta added that the government had honored its pledge to expand recruitment and improve the training and welfare of Kenyan security personnel.
"Similarly, we have invested in equipment – in vehicles, as well as technology required by our security agencies – to tackle insecurity," he asserted.
He went on to warn Kenyan politicians against engaging in what he called "sideshows" in matters pertaining to national security.
The president added that his country was fighting a "proxy war" and that it expected "solidarity and robust engagement" to confront both internal and external terrorism.
"If you [the Kenyan opposition] have issues with steps taken by [my] government in dealing with terrorism, use relevant institutions instead of engaging in sideshows," he said.
"No freedom has been curtailed in the proposed amendment of the security bill," he claimed, referring to new legislation currently being debated in parliament.
He said the government was opposed to the publication of images of victims in Kenyan media, saying such images only encouraged Kenya's enemies.
A large number of politicians from Kenya's main opposition party, the Coalition for Reforms and Democracy, also attended Friday's event.
Attending politicians included Raila Amolo Odinga, Kalonzo Musyoka and Moses Wetangula.
The trio's presence at the event came in the wake of a debate among Kenyan lawmakers over proposed security legislation, which would empower Kenyan security agencies.
Among other things, the legislation would grant the president the right to dismiss under-performing security chiefs.
It would also open the door for stepped-up surveillance to apprehend suspects and allow police and intelligence officers to stop suspects before they carry out attacks.
The legislation, however, would limit freedom of speech, curtail the right to privacy by permitting phone taps, and oblige media houses to get authorization from police before printing photographs of terrorism victims.
Opposition leaders have threatened to stage mass protests and take legal action to prevent parliament from approving the controversial legislation.
Speaking to reporters in Nairobi on Friday, opposition leader Raila Odinga said Kenyatta – along with his deputy, William Ruto – was "attempting to open new avenues for authoritarianism by turning Kenya into a police state."
"We plan to ask Kenyans to rise up against this law, which is aimed at turning Kenya into a dictatorship," warned Odinga.