US authorities have issued a warning of a possible terrorist threat around the 4th of July holiday weekend. A joint intelligence bulletin was issued by the Department of Homeland Security, the FBI and the National Counterterrorism Center on 26 June to law enforcement around the country.

According to CNN, the bulletin does not warn of any known active plots, but instead serves as a general warning. The warning states that terrorist could launch attacks tied to the country's celebration of Independence Day or in response to perceived defamation of Islam's Prophet Mohammed.

US law enforcement officials have noted that Islamist terrorist threat is at the highest level in years, CNN reported. Authorities have increased the arrests and charges on homegrown extremists believed to be plotting attacks or supporting terror organisations such as Isis.

The bulletin comes on the heels of three major Islamist terror attacks in Tunisia, Kuwait and France. Department of Homeland Security Secretary Jeh C Johnson released a statement on 26 June regarding the three terrorist attacks.

"Today's terrorist attacks in France, Tunisia and Kuwait are a reminder of the evolving global terrorist threats. We stand in support of the people of those countries and mourn the loss of those killed," Johnson said.

He continued, "Particularly with the upcoming July 4th holiday, here in the United States the Department of Homeland Security and the FBI continue to communicate with state and local law enforcement about what we know and see. We are encouraging all law enforcement to be vigilant and prepared. We will also adjust security measures, seen and unseen, as necessary to protect the American people."

As previously reported by IBTimes UK, security will also be stepped up in London on 27 June during two major events: Armed Forces Day and Pride Festival.

"The UK threat level remains as severe. I am announcing additional security measures at events over the weekend, including Armed Forces Day and Pride London. The security of these events comes under constant review," Metropolitan Police Deputy Assistant Commissioner Helen Ball said.