The chairman of the Senate Foreign Relations Committee was in Sudan on Sunday for the historic referendum on splitting the Christian south from the Muslim northern part of the country.

The referendum, which many lawmakers have feared could erupt into fresh violence in the country scarred by genocide, is part of the 2005 comprehensive peace agreement to end more than two decades of bloody civil war.

"I am extraordinarily honored and privileged to be here to share this moment," Sen. John KerryJohn Forbes KerryShould President Trump, like President Obama, forsake human rights in pursuit of the deal with a tyrant? GOP Senate report says Obama officials gave Iran access to US financial system Democrats conflicted over how hard to hit Trump on Iran MORE (D-Mass.) said in a statement. "And what we have seen thus far has been magnificent. I saw long lines of people waiting for hours but reveling in the privilege of voting for their freedom. When I mentioned to some voters the need to be patient, they said we have waited 55 years, we can wait a few more hours."

At a church service Sunday morning with President Salva Kiir of Southern Sudan, Kerry, on his fourth trip to Sudan, told attendees "the moment has arrived where the hard work of preparing can become the hard work of turning dreams into reality."

"And today I can assure you, President Obama, the Congress and the American people share your hope for the future and your faith in the values that will lead you there," Kerry said. "I am proud to convey to you the unwavering support of the United States for your efforts to build your new nation."

Deadly clashes were reported along Sudan's north-south border Saturday, including in the disputed flashpoint of Abyei, which isn't participating in the vote. A referendum on the fate of the disputed region was supposed to coincide with the secession vote but has been delayed.

The southern secesssion vote began Sunday and will last for a week. Turnout is said to be exceeding that of legislative elections.

About 1,400 international poll observers have been deployed across the country, including former President Carter and former U.N. Secretary-General Kofi Annan.

On Monday, Rep. Frank WolfFrank Rudolph WolfVulnerable Republican keeps focus as Democrats highlight Trump Bolton could be the first national security chief to prioritize religious freedom House votes to mandate sexual harassment training for members and staff MORE (R-Va.), co-chairman of the bipartisan Sudan Caucus in the House, visited an out-of-country voting center where Sudanese were voting in Alexandria, Va.

The longtime Sudan advocate was joined by Leonard Leo, chairman of the U.S. Commission on International Religious Freedom (USCIRF), and USCIRF Commissioner Nina Shea. USCIRF delegations have visited Sudan three times over the past year alone and have made a series of key Sudan policy recommendations in the lead-up to the referendum.

"All sides should refrain from inflammatory rhetoric or provocative actions that could raise tensions or prevent voters from expressing their will. Violence in the Abyei region should cease," President Obama said in a Sunday statement. "And while a successful vote will be cause for celebration, an enormous amount of work remains to ensure the people of Sudan can live with security and dignity.

"The world will be watching in the coming days, and the United States will remain fully committed to helping the parties solve critical post-referendum issues regardless of the outcome of the vote," he said.

—This story was updated Monday at 3:25 p.m.