U.S. President Barack Obama's job approval rating has increased to 50 percent, extending his lead over his top Republican challenger Mitt Romney, according to two Gallup polls released Tuesday.

While Obama's approval rating climbed to 50 percent, his disapproval rating dropped to 44 percent, according to April 21-23 Gallup Daily tracking poll on Obama's support among U.S. voters.

The 50-percent approval rating during the April 21-23 Gallup Daily tracking poll is notable because all incumbent U.S. presidents since Dwight Eisenhower who were at or above this mark at the time of the election were re-elected. Obama's approval rating has typically been in the mid-40 percent range for the last three months, the Gallup said in a report on the polls.

One possible reason for the increase in Obama's approval rating is the recent decline in gas prices, rises of which have often been associated with a decline in presidential approval ratings, the Gallup said.

At the same time, Obama held a lead of 49-42 percent in the April 19-23 Gallup Daily tracking poll over Romney, who is widely expected to secure his nomination soon after the Republican primaries in five states held Tuesday.

The seven-percentage-point Obama advantage, which marks a shift from last week when Romney held an edge, also represents the largest lead Obama has held over Romney in the Gallup Daily tracking poll since August.

Obama's lead is owing in large part to his improved standing among independent voters. In the April 11-15 Gallup tracking, Romney was leading Obama by 45-39 percent among independent voters. Obama now holds a 45-43 percent advantage among this group, the Gallup said.

In recent days, Americans have become more positive about the job Obama is doing as president, and at the same time now prefer him by a significant margin over Romney in the fall election.

Although the readings on these measures are likely to change again in the days and weeks ahead, they suggest at the moment a solid footing for the Obama re-election campaign, the Gallup said.

 VietNamNet/Xinhuanet