WASHINGTON  -- The US Senate passed a landmark comprehensive immigration bill on Thursday that would offer an earned citizenship for about 11 million undocumented immigrants and tighten security on the Mexican border.

The bill, approved in the Senate after three weeks of debate on the floor and months of negotiations, now advances to even greater uncertainties in the House of Representatives, where many oppose citizenship for illegal immigrants.

MONTHS OF EFFORTS

Vice President Joe Biden, who presided the roll call from the Senate's dais, announced that the bill had been approved by 68 to 32, more than the majority needed to send the measure to the House.

Fourteen of the 46 Republicans in the 100-member chamber joined all 52 Democrats and two independents to support the bill, which tops President Barack Obama's second-term domestic agenda.

Senate Judiciary Committee Chairman Patrick Leahy hailed the vote which marked an end to years of bipartisan gridlock on immigration, saying "Today is another historic day in the Senate."

Sponsors of the bill believed that the Senate's approval may serve as the biggest boost in decades for the issue of immigration overhaul to become legislation.

"Make no mistake about it, the support this bill has generated here in the Senate will be impossible to ignore," Senator Charles Schummer, the lead Democratic sponsor, said before the vote. "I believe the support the bill will receive today in the Senate will propel it to pass the House and be placed for signature on the president's desk by the end of the year."

The bill was drafted and sponsored by a bipartisan group of Senators, dubbed as Gang of Eight. The group includes top-ranking Democrats and leading Republicans on immigration reforms like veteran Senator John McCain and Hispanic Republican star Marco Rubio.

The bill, which was unveiled in April and has so far received the most attention nationwide, echoes the goals set by the president since the very beginning of his second term. Both of their agenda include giving an earned citizenship to 11 million undocumented immigrants currently living in the country, toughening border security as well as awarding green cards to high- skilled foreign workers.

OBAMA'S TOP AGENDA

Obama, on a visit to Africa, moved quickly to applaud the Senate's approval.

"Today, with a strong bipartisan vote, the United States Senate delivered for the American people, bringing us a critical step closer to fixing our broken immigration system once and for all," said Obama in a statement.

The president, however, urged the Congress to "finish its job." "Today, the Senate did its job. It's now up to the House to do the same," he said.

Obama also warned those stakeholders to "keep a watchful eye" over the immigration overhaul, which is well expected to meet greater resistance in the House.

"Now is the time when opponents will try their hardest to pull this bipartisan effort apart so they can stop common-sense reform from becoming a reality. We can not let that happen," he said.

Obama said that the Senate bill, if enacted, would establish " the most aggressive border security plan in our history." It was the measure that has helped secure Republican support needed to pass the bill through the Senate.

The US demographic landscape is undergoing a major shift as the current minority communities continue to grow while the whites could become minority in the next three decades, according to US census.

Hispanics, a fast-growing group in particular, is a huge target group that Democrats hope to secure and Republicans aspire to win back in future elections. Latino-Americans voted for Obama over Republican challenger Mitt Romney 71 percent to 27 percent in the 2012 presidential race.

The White House is now trying to keep focus on Obama's second- term agenda, while major controversies have dominated the headlines in recent weeks, including the National Security Agency' s secret surveillance programs disclosed by 30-year-old defense contractor employee Edward Snowden.

ROCKY ROAD AHEAD

The past decade or so saw several unsuccessful bids to overhaul a US immigration law enacted in 1986.

Advocates for immigration reform now see a decent chance for legislation to pass through the Capitol Hill this year.

Although it has passed the Democratic-controlled Senate with a bipartisan support, the bill will still have a longer and tougher way to go in the Republican-dominated House.

The overhaul, which offers a 13-year path to citizenship to millions of undocumented immigrants, has been opposed by many Republicans in the lower chamber.

House Speaker John Boehner said in the day that the House would not simply take up and vote on the Senate bill.

"For any legislation, including a conference report, to pass the House, it's going to have to be a bill that has the support of a majority of our members," he said.

Although some House Republicans have said a bill could be on the floor some time in July, Boehner declined to say when the full House might debate and vote on an immigration bill.

He said he will huddle with his fellow Republicans following a July 4 recess.