Al-Qaida linked gunmen have largely taken over the cities of Fallujah and Ramadi in an uprising that has been a blow to the Shiite-led government of Iraqi Prime Minister Nouri al-Maliki. Bombings in the Iraqi capital, Baghdad, killed at least 20 people Sunday.
Anbar, a vast desert area on the borders with Syria and Jordan, was the heartland of the Sunni insurgency that rose up against American troops and the Iraqi government after the 2003 U.S.-led invasion that toppled Saddam Hussein.
In 2004, insurgents in Fallujah killed four American security contractors, hanging their burned bodies from a bridge. Ramadi and other cities have remained battlegrounds as sectarian bloodshed has mounted, with Shiite militias killing Sunnis.
"We are very, very concerned about the efforts of al-Qaida and the Islamic State of Iraq in the Levant, which is affiliated with al-Qaida, who are trying to assert their authority not just in Iraq, but in Syria," Kerry said.
"These are the most dangerous players in that region. Their barbarism against the civilians in Ramadi and Fallujah and against Iraqi security forces is on display for everyone in the world to see."
Kerry made the comments as he left Jerusalem for talks with leaders in Jordan and Saudi Arabia about his Mideast peace-making efforts after three days of lengthy meetings with Palestinian President Mahmoud Abbas and Israeli Prime Minister Benjamin Netanyahu.
Kerry said some progress was made in what he described as "very serious, very intensive conversations," but key hurdles are yet to be overcome.
His talks with Jordan's King Abdullah II and Foreign Minister Nasser Judeh covered the peace process, Syria and Iraq.
After his short stay in Amman, Kerry flew to Riyadh, Saudi Arabia, and then took a 30-minute helicopter ride to King Abdullah's desert palace.
The Saudi leader developed an initiative in 2002 in which the Arab world offered comprehensive peace with Israel in exchange for a full pullout from all territories it captured in the 1967 Mideast war.
The initiative, revolutionary when it was introduced, has been endorsed by the Arab League and, technically, remains in effect.
"Saudi Arabia's initiative holds out the prospect that if the parties could arrive at a peaceful resolution, you could instantaneously have peace between the 22 Arab nations and 35 Muslim nations, all of whom have said they will recognize Israel if peace is achieved," Kerry said.
"Imagine how that changes the dynamics of travel, of business, of education, of opportunity in this region, of stability. Imagine what peace could mean for trade and tourism, what it could mean for developing technology and talent, for job opportunities for the younger generation, for generations in all of these countries," Kerry said.
Kerry, who arrived in the region Thursday, is trying to nudge Abbas and Netanyahu closer to a peace pact that would establish a Palestinian state alongside Israel.
The talks have entered an intense phase aimed at getting the two sides to agree on a framework and provide guidance toward a final settlement. Reaching a deal on that framework is not expected on this trip, Kerry's 10th to the region for peace talks.