HOUSTON -- The Nationals agreed to terms with four international free agents on Monday, one right-handed pitcher and three outfielders.

General manager Mike Rizzo and director of international scouting Johnny DiPuglia announced the signings of right-hander Ramses Rosario and outfielders Aldrem Corredor, Darryl Florentino and Luis Guzman.

Rosario is a 6-foot-3, 175-pound 16-year-old from Venezuela. According to a club release, Rosario features three quality pitches and has "advanced pitching instincts."

Corredor, also a 16-year-old from Venezuela, bats lefty and can play both corner-outfield positions. Florentino, 16, is 6-foot-2, 180 pounds and regarded as a speedy, high-quality defender with a strong throwing arm.

The Nationals say the 6-foot-1, 183-pound Guzman, a native of the Dominican Republic, should be a prototypical leadoff hitter with some power on offense and potentially plus defense.

Injured Desmond takes grounders, throws

HOUSTON -- Ian Desmond took a step forward on Monday in his rehab from a torn left oblique, fielding grounders and making throws at shortstop before the Nationals' series opener against the Astros at Minute Maid Park.

Desmond reported that he was feeling good, and while manager Davey Johnson is pleased by Desmond's progress, he's not in any hurry to push up the timetable for the All-Star shortstop's return.

Desmond has been running for about a week, but Monday was his first time doing work in the infield. Still, Johnson didn't expect Desmond to start hitting for 10 days to two weeks.

"All that is good," Johnson said. "And he feels great.

"I don't really know how to treat obliques, but I'm going to treat it like I would a hamstring, and that's very cautiously," he added. "You don't rush him back, because if you re-injure him, it's double the time. I think it's good that he's doing some things, especially aerobically. ... It gives him a chance to let his body heal."

Werth feeling good, swinging hot bat since return

HOUSTON -- As far as Nationals manager Davey Johnson was concerned, Jayson Werth had the day off on Monday. That is to say, he wasn't playing center field -- he was starting in right field and batting sixth.

Werth has jumped right back into the swing of things since coming off the disabled list last week. He's played every day -- although not every game, as he only started Game 1 of Friday's doubleheader -- and hit well. Werth has gone 5-for-12 with five walks and only one strikeout in four games since returning, and he's yet to report any soreness after missing 75 games with a broken left wrist.

"I feel good. It's a little surprising. Everything happened so fast," Werth said on Sunday. "I went from not being able to swing to here in like 10 days. I feel strong. I'm just glad to be back and part of the club.

"It's surprising, really, to suffer that kind of injury and be out for three months or whatever, then the last two weeks, all of a sudden it just shows up and it's ready to go."

Werth may have surprised himself, but not Johnson. The skipper said he could tell in Spring Training that Werth was back on track after a disappointing 2011, and the way he's been swinging the bat since his return has only reinforced that opinion.

"Actually, he is more aggressive and more hungry coming back than he was when he started the year," Johnson said. "He's been attacking the ball. I like that. I like what I'm seeing. I don't think he's probably 100 percent there yet."

Werth left Monday's 5-4 win against the Astros in the eighth inning because, Johnson said, his legs were tightening up. Werth said it was nothing, and he planned to be back on the field Tuesday.