BAGHDAD , Iraq -LRB- CNN -RRB- -- The highly fortified International Zone in Baghdad came under fire the same day that Vice President Joe Biden paid a surprise visit , an Interior Ministry official told CNN . Vice President Joe Biden talks to the media Tuesday in Baghdad 's fortified International Zone . Biden was not injured , according to CNN 's Chris Lawrence , who was traveling with the vice president . But at least one round seems to have landed in the U.S. Embassy grounds , U.S. Ambassador Christopher Hill said . The zone houses the embassy and many government buildings . Lawrence said he heard the blasts but saw no damage . CNN 's Cal Perry said he heard four loud `` booms . '' Warning alarms were sounded , and security was stepped up in the International Zone , which is informally known as the Green Zone . It is not clear what weapons were fired or if Biden was near the location where the rounds hit . For security reasons , reporters traveling with the vice president are not allowed to report his location . Watch as Lawrence reports on the attack '' A U.S. military spokesman said he could confirm only that one round hit , and he said it did not land in the International Zone . `` Initial reports indicate one round of indirect fire impacted near the International Zone , not in it , '' Lt. Col. Phillip Smith , a spokesman for the U.S. military in Baghdad , told CNN . But Hill told reporters that some sort of projectile landed in the east end of the embassy complex . He said the projectile was the reason for a `` duck-and-cover '' alarm that journalists traveling with Biden heard during a briefing by top U.S. officials in Baghdad . The alarm sounded intermittently throughout almost the entire 35-minute briefing by Hill and the top U.S. general in Iraq , Ray Odierno , Lawrence said . Odierno and Hill did not seem concerned , he said . No one jumped up or tried to run out of the building . They paused if they were talking when the alarm sounded , and picked up when it stopped . There was an `` all-clear '' as the briefing ended . Hill said it is kind of unusual to get this type of attack now . He said they used to happen 10 to 12 times a day , but now are few and far between . Biden 's visit was widely reported on Iraqi television , Perry said . He is in Iraq to meet with the country 's leaders and visit U.S. troops , his office said . Journalists on the plane with the vice president were not told where they were going until after they were on the way . Biden was due to sit down with Iraqi President Jalal Talabani and Prime Minister Nuri al-Maliki , as well as Massoud Barzani , the president of the Kurdistan Regional Government , and other officials . He was greeted at the airport at dusk by Gen. Odierno , Ambassador Hill and Iraqi Foreign Minister Hoshyar Zebari . Watch Biden arrive in Iraq , greet troops '' He flew by helicopter to the International Zone . Biden , Hill , Odierno and Deputy Secretary of State Jim Steinberg , who is traveling with Biden , then went into a meeting . They did not speak to reporters . This is Biden 's third trip to Iraq this year , after visits in July and January . `` The president has asked the vice president to provide sustained , high-level focus from the White House on Iraq , and this trip is part of that mission , '' the White House said in a statement issued as Biden arrived . The United States is less than a year away from its goal of withdrawing all combat troops from Iraq . Hill has said the next 12 months are `` very critical '' to establishing security in Iraq , but the goal of withdrawing most U.S. troops by August 2010 is `` absolutely achievable . '' Biden said Odierno is `` optimistic '' that Iraqi forces will be ready in time to allow U.S. withdrawals to go ahead as planned , according to Lawrence . CNN 's Jomana Karadsheh contributed to this report .